Archive for August, 2011

This is a list of papers on permanent El Niño-like conditions. The list is not complete, and will most likely be updated in the future in order to make it more thorough and more representative.

Pliocene (5-3 Ma)

Implications of the permanent El Niño teleconnection “blueprint” for past global and North American hydroclimatology – Goldner et al. (2011) “Substantial evidence exists for wetter-than-modern continental conditions in North America during the pre-Quaternary warm climate intervals. This is in apparent conflict with the robust global prediction for future climate change of a northward expansion of the subtropical dry zones that should drive aridification of many semiarid regions. Indeed, areas of expected future aridification include much of western North America, where extensive paleoenvironmental records are documented to have been much wetter before the onset of Quaternary ice ages. It has also been proposed that climates previous to the Quaternary may have been characterized as being in a state with warmer-than-modern eastern equatorial sea surface temperatures (SSTs). Because equatorial Pacific SSTs exert strong controls on midlatitude atmospheric circulation and the global hydrologic cycle, the teleconnected response from this permanent El Niño-like mean state has been proposed as a useful analogue model, or “blueprint”, for understanding global climatological anomalies in the past. The present study quantitatively explores the implications of this blueprint for past climates with a specific focus on the Miocene and Pliocene, using a global climate model (CAM3.0) and a nested high-resolution climate model (RegCM3) to study the hydrologic impacts on global and North American climate of a change in mean SSTs resembling that which occurs during modern El Niño events. We find that the global circulation response to a permanent El Niño resembles a large, long El Niño event. This state also exhibits equatorial super-rotation, which would represent a fundamental change to the tropical circulations. We also find a southward shift in winter storm tracks in the Pacific and Atlantic, which affects precipitation and temperature over the mid-latitudes. In addition, summertime precipitation increases over the majority of the continental United States. These increases in precipitation are controlled by shifts in the subtropical jet and secondary atmospheric feedbacks. Based on these results and the data proxy comparison, we conclude that a permanent El Niño like state is one potential explanation of wetter-than-modern conditions observed in paleoclimate-proxy records, particularly over the western United States.” Goldner, A., Huber, M., Diffenbaugh, N., and Caballero, R.: Clim. Past, 7, 723-743, doi:10.5194/cp-7-723-2011, 2011. [Full text]

Teleconnections in a warmer climate: the pliocene perspective – Shukla et al. (2011) “Migrations toward altered sea surface temperature (SST) patterns in the Indo-Pacific region are present in the recent observational record and in future global warming projections. These SSTs are in the form of “permanent” El Niño-like (herein termed “El Padre”) and Indian Ocean Dipole (IOD)-like patterns. The Early Pliocene Warm Period, which bears similarity to future warming projections, may have also exhibited these Indo-Pacific SST patterns, as suggested by regional terrestrial paleo-climatic data and general circulation model studies. The ability to corroborate this assessment with paleo-data reconstructions is an advantage of the warm Pliocene period that is not afforded by future warming scenarios. Thus, the Pliocene period provides us with a warm-climate perspective and test bed for understanding potential changes to future atmospheric interactions given these altered SST states. This study specifically assesses how atmospheric teleconnections from El Padre/IOD SST patterns are generated and propagate to create the regional climate signals of the Pliocene period, as these signals may be representative of future regional climatic changes as well. To do this, we construct a holistic diagnostic rubric that allows us to examine atmospheric teleconnections, both energetically and dynamically, as produced by a general circulation model. We incorporate KE′, a diagnostic adapted from the eddy kinetic energy generation field, to assess the available energy transferred to these teleconnections. Using this methodology, we found that relative to our Modern Control experiments, weaker atmospheric teleconnections prevail under warm Pliocene conditions, although pathways of propagation still appear directed toward the southwestern United States from our tropical Pacific sector forcing. Propagation directly emanating from the Indian Ocean forcing sector appears to be largely blocked, although indirect teleconnective pathways appear traversing the Asian continent toward the North Pacific. The changes in the atmospheric circulation of Indian Ocean region in response to the underlying specified SST forcing (and indicated by Pliocene paleo-data) may have a host of implications for energy transfer out of and into the region, including interactions with the Asian jet stream and changes to the seasonal monsoon cycle. These interactions warrant further study in both past and future warm climate scenarios.” Sonali P. Shukla, Mark A. Chandler, David Rind, Linda E. Sohl, Jeff Jonas and Jean Lerner, Climate Dynamics, DOI: 10.1007/s00382-010-0976-y.

Permanent El Niño and the onset of Northern Hemisphere glaciations: Mechanism and comparison with other hypotheses – Vizcaíno et al. (2010) “The tropical Pacific transitioned from a “permanent El Niño” state, that is, without the current equatorial zonal gradient of sea surface temperatures, to one with an equatorial cold tongue in a process that started ∼4 Ma, during the early Pliocene. The latter stages of this transition, around ∼2.75 Ma, marked the onset of Northern Hemisphere glaciations. We explore the hypothesis that this onset of glaciation is causally linked to the development of the cold tongue guided by atmosphere general circulation model (AGCM) simulations forced by various hypothesized climate influences. A unique feature of our simulations is imposing permanent El Niño conditions not by imposing sea surface temperatures anomalies directly but rather through changing the implied ocean heat transport in the slab ocean component of the AGCM, done in such a way as to maintain global ocean heat balance. Similar to previous studies, we find increased near-surface temperature conditions occur during simulated permanent El Niño conditions at the locations of known ice sheet growth during glacial periods. We establish that this tropical-extratropical connection is mediated through atmospheric stationary waves, a well-known atmospheric pathway for today’s El Niño influence on North America. The influence of the permanent El Niño condition is compared, through model simulations, to other mechanisms proposed to date to explain the onset of glaciations at ∼2.75 Ma: changes in atmospheric carbon dioxide (CO2) concentrations, closure of the Panama seaway, and changes in North Pacific seasonality. The exact comparison is done by calculating differences in the equilibrium line altitude at the known locations of ice sheet growth, an approach that permits the translation of climate anomalies into a measurement of glaciation trends in terms of glacier mass balance. We find that permanent El Niño and atmospheric CO2 are the leading influences in this comparison, leading us to conjecture that the two influences combined determined the long-term background conditions governing ice sheet growth. Within this long-term background evolution, however, we additionally find that the exact timing of Northern Hemisphere glaciations is likely to have come from favorable orbital conditions. Our results regarding permanent El Niño on Northern Hemisphere glaciations is, however, conditioned on a strong sensitivity of Northern Hemisphere climate changes to how the oceanic heat compensation to the permanent El Niño is achieved.” Vizcaíno, M., S. Rupper, and J. C. H. Chiang (2010), Paleoceanography, 25, PA2205, doi:10.1029/2009PA001733. [Full text]

Tropical cyclones and permanent El Niño in the early Pliocene epoch – Fedorov et al. (2010) “Tropical cyclones (also known as hurricanes and typhoons) are now believed to be an important component of the Earth’s climate system. In particular, by vigorously mixing the upper ocean, they can affect the ocean’s heat uptake, poleward heat transport, and hence global temperatures. Changes in the distribution and frequency of tropical cyclones could therefore become an important element of the climate response to global warming. A potential analogue to modern greenhouse conditions, the climate of the early Pliocene epoch (approximately 5 to 3 million years ago) can provide important clues to this response. Here we describe a positive feedback between hurricanes and the upper-ocean circulation in the tropical Pacific Ocean that may have been essential for maintaining warm, El Niño-like conditions during the early Pliocene. This feedback is based on the ability of hurricanes to warm water parcels that travel towards the Equator at shallow depths and then resurface in the eastern equatorial Pacific as part of the ocean’s wind-driven circulation. In the present climate, very few hurricane tracks intersect the parcel trajectories; consequently, there is little heat exchange between waters at such depths and the surface. More frequent and/or stronger hurricanes in the central Pacific imply greater heating of the parcels, warmer temperatures in the eastern equatorial Pacific, warmer tropics and, in turn, even more hurricanes. Using a downscaling hurricane model, we show dramatic shifts in the tropical cyclone distribution for the early Pliocene that favour this feedback. Further calculations with a coupled climate model support our conclusions. The proposed feedback should be relevant to past equable climates and potentially to contemporary climate change.” Alexey V. Fedorov, Christopher M. Brierley & Kerry Emanuel, Nature 463, 1066-1070 (25 February 2010) | doi:10.1038/nature08831. [Full text]

Impact of a permanent El Niño (El Padre) and Indian Ocean Dipole in warm Pliocene climates – Shukla et al. (2009) “Pliocene sea surface temperature data, as well as terrestrial precipitation and temperature proxies, indicate warmer than modern conditions in the eastern equatorial Pacific and imply permanent El Niño–like conditions with impacts similar to those of the 1997/1998 El Niño event. Here we use a general circulation model to examine the global-scale effects that result from imposing warm tropical sea surface temperature (SST) anomalies in both modern and Pliocene simulations. Observed SSTs from the 1997/1998 El Niño event were used for the anomalies and incorporate Pacific warming as well as a prominent Indian Ocean Dipole event. Both the permanent El Niño (also called El Padre) and Indian Ocean Dipole (IOD) conditions are necessary to reproduce temperature and precipitation patterns consistent with the global distribution of Pliocene proxy data. These patterns may result from the poleward propagation of planetary waves from the strong convection centers associated with the El Niño and IOD.” Shukla, S. P., M. A. Chandler, J. Jonas, L. E. Sohl, K. Mankoff, and H. Dowsett (2009), Paleoceanography, 24, PA2221, doi:10.1029/2008PA001682. [Full text]

Warm-water mollusc assemblages from northern Chile (Mejillones Peninsula): new evidence for permanent El Niño-like conditions during Pliocene warmth? – Ragaini et al. (2008) “Although results have been controversial, understanding the tropical Pacific climatic state during the Pliocene warm interval (c. 4.5–3.0 Ma) is crucial if insight is to be gained into the dynamic processes of present and future global warming. In the multi-proxy effort to reconstruct ancient climates, a critical role can be played by palaeoclimatic evidence provided by the spatial and temporal distribution of temperature-sensitive marine molluscs. Shallow-water strata of the Mejillones Peninsula, northern Chile (23°S), contain dense faunal assemblages in which molluscs exclusive to, or characteristic of, Pliocene deposits (Chlamys simpsoni, Chlamys vidali, Chorus blainvillei, Concholepas nodosa, Fusinus remondi, Herminespina mirabilis) coexist with surprisingly abundant and varied populations of extant warm-water species (Bulla punctulata, Cerithium stercusmuscarum, Olivella sp., Turbo cf. fluctuosus, Anomia peruviana, Argopecten ventricosus, Donax peruvianus, Dosinia ponderosa, Mexicardia procera, Undulostrea megodon), most of which have their current southern zoogeographical limit at 6°S. These tropical elements are reliable indicators of nearshore marine conditions and their abundant occurrence implies that sea surface temperatures (SST) along the northern Chile coast were at least 2 °C warmer in the mid-Pliocene than at present, and that these very different conditions lasted long enough to allow stable colonization of the area. Such a significantly warmer SST pattern strongly resembles general climatic conditions accompanying modern El Niño events, when warm tropical waters propagate southward along the western margin of South America; this supports the existence in this area of persistently El Niño-like conditions during the mid-Pliocene.” Luca Ragaini, Claudio Di Celma and Gino Cantalamessa, Journal of the Geological Society; December 2008; v. 165; no. 6; p. 1075-1084; DOI: 10.1144/0016-76492007-039.

A permanent El Niño–like state during the Pliocene? – Haywood et al. (2007) “The Pliocene may have been characterized by permanent El Niño–like conditions. Initial modeling studies suggest that this may have contributed to Pliocene warmth. The termination of this state may have influenced Northern Hemisphere glaciation (NHG). We use the Hadley Centre Coupled Model version 3 to examine the role of the oceans and ocean structure on Pliocene warmth. A permanent El Niño–like state is not predicted. Annual mean sea surface temperatures in the eastern equatorial Pacific at Ocean Drilling Program Sites 847 and 851 increase by 1.71°C and 1.15°C, respectively. However, El Niño Southern Oscillation events are clearly expressed by the model. Sensitivity tests indicate that a prescribed permanent El Niño–like condition increases annual global mean surface temperatures by a maximum of 0.6°C. If the Pliocene was characterized by such a condition, it is questionable that it provided a major contribution to global warmth and therefore unlikely that the termination of this state contributed significantly to the onset of NHG.” Haywood, A. M., P. J. Valdes, and V. L. Peck (2007), Paleoceanography, 22, PA1213, doi:10.1029/2006PA001323. [Full text]

Early Pliocene (pre–Ice Age) El Niño–like global climate: Which El Niño? – Molnar & Cane (2011) “Paleoceanographic data from sites near the equator in the eastern and western Pacific Ocean show that sea-surface temperatures, and apparently also the depth and temperature distribution in the thermocline, have changed markedly over the past ∼4 m.y., from those resembling an El Niño state before ice sheets formed in the Northern Hemisphere to the present-day marked contrast between the eastern and western tropical Pacific. In addition, differences between late Miocene to early Pliocene (pre–Ice Age) paleoclimates and present-day average climates, particularly in the Western Hemisphere, resemble those associated with teleconnections from El Niño events, consistent with the image of a permanent El Niño state. Agreement is imperfect in that many differences between early Pliocene and present-day climates of parts of Africa, Asia, and Australia do not resemble the anomalies associated with canonical El Niño teleconnections. The teleconnections associated with the largest El Niño event in the past 100 yr, that in 1997–1998, do, however, reveal similar patterns of warming and the same sense, if not magnitude, of precipitation anomalies shown by differences between late Miocene-early Pliocene paleoclimates and present-day mean climates in these regions. If less consistent than those for the 1997–1998 event, temperature and precipitation anomalies correlated with the Pacific Decadal Oscillation also mimic many differences between early Pliocene and present-day climates. These similarities suggest that the sea-surface temperature distribution in the Pacific Ocean before Ice Age time resembled most that of the 1997–1998 El Niño, with the warmest region extending into the easternmost Pacific Ocean, not near the dateline as occurs in most El Niño events. This inference is consistent with equatorial Pacific proxy data indicating that at most a small east-west gradient in sea-surface temperature seems to have existed along the equator in late Miocene to early Pliocene time. Accordingly, such a difference in sea-surface temperatures may account for the large global differences in climate that characterized the earth before ice sheets became frequent visitors to the Northern Hemisphere.” Peter Molnar and Mark A. Cane, Geosphere, v. 3 no. 5 p. 337-365, doi: 10.1130/GES00103.1.

Warm upwelling regions in the Pliocene warm period – Dekens et al. (2007) “Given the importance of upwelling processes to coastal productivity and regional climate, it is critical to study the role of upwelling regions within the context of global climate change. We generated sea surface temperature (SST) records for the last 5 million years in three important upwelling regions: the eastern equatorial Pacific, the California margin, and the Peru margin. Prior to ∼3.0 Ma, SSTs at all sites were significantly warmer than today (by 3–9°C), indicating that cold upwelling regions that characterize the modern Pacific Ocean did not exist in the early Pliocene warm period (4.6 to 3.1 Ma), Earth’s most recent period of sustained global warmth. Alkenone, phosphorus, and organic carbon mass accumulation rate records indicate that changes in productivity and SST were decoupled and that upwelling of nutrient enriched water occurred even when SSTs were warm during the early Pliocene. Thus the long-term trends in SST are likely explained by changes in the temperature of upwelled water rather than in the strength of upwelling-favorable winds alone. The fact that gradual cooling of upwelling regions began before the onset of significant Northern Hemisphere glaciation provides further evidence that the growth of ice sheets and their influence on atmospheric winds alone can not explain the cooling of upwelling regions. Our results suggest that the long-term average SSTs of upwelling regions are influenced by global changes in the depth and/or temperature of the ventilated thermocline.” Dekens, P. S., A. C. Ravelo, and M. D. McCarthy (2007), Paleoceanography, 22, PA3211, doi:10.1029/2006PA001394.

The Pliocene Paradox (Mechanisms for a Permanent El Niño) – Fedorov et al. (2006) “During the early Pliocene, 5 to 3 million years ago, globally averaged temperatures were substantially higher than they are today, even though the external factors that determine climate were essentially the same. In the tropics, El Niño was continual (or “permanent”) rather than intermittent. The appearance of northern continental glaciers, and of cold surface waters in oceanic upwelling zones in low latitudes (both coastal and equatorial), signaled the termination of those warm climate conditions and the end of permanent El Niño. This led to the amplification of obliquity (but not precession) cycles in equatorial sea surface temperatures and in global ice volume, with the former leading the latter by several thousand years. A possible explanation is that the gradual shoaling of the oceanic thermocline reached a threshold around 3 million years ago, when the winds started bringing cold waters to the surface in low latitudes. This introduced feedbacks involving ocean-atmosphere interactions that, along with ice-albedo feedbacks, amplified obliquity cycles. A future melting of glaciers, changes in the hydrological cycle, and a deepening of the thermocline could restore the warm conditions of the early Pliocene.” A. V. Fedorov, P. S. Dekens, M. McCarthy, A. C. Ravelo, P. B. deMenocal, M. Barreiro, R. C. Pacanowski and S. G. Philander, Science 9 June 2006: Vol. 312 no. 5779 pp. 1485-1489, DOI: 10.1126/science.1122666.

Cool La Niña During the Warmth of the Pliocene? – Rickaby & Halloran (2005) “The role of El Niño–Southern Oscillation (ENSO) in greenhouse warming and climate change remains controversial. During the warmth of the early-mid Pliocene, we find evidence for enhanced thermocline tilt and cold upwelling in the equatorial Pacific, consistent with the prevalence of a La Niña–like state, rather than the proposed persistent warm El Niño–like conditions. Our Pliocene paleothermometer supports the idea of a dynamic “ocean thermostat” in which heating of the tropical Pacific leads to a cooling of the east equatorial Pacific and a La Niña–like state, analogous to observations of a transient increasing east-west sea surface temperature gradient in the 20th-century tropical Pacific.” R. E. M. Rickaby and P. Halloran, Science 25 March 2005: Vol. 307 no. 5717 pp. 1948-1952, DOI: 10.1126/science.1104666. [Full text]

Permanent El Niño-Like Conditions During the Pliocene Warm Period – Wara et al. (2005) “During the warm early Pliocene (∼4.5 to 3.0 million years ago), the most recent interval with a climate warmer than today, the eastern Pacific thermocline was deep and the average west-to-east sea surface temperature difference across the equatorial Pacific was only 1.5 ± 0.9°C, much like it is during a modern El Niño event. Thus, the modern strong sea surface temperature gradient across the equatorial Pacific is not a stable and permanent feature. Sustained El Niño-like conditions, including relatively weak zonal atmospheric (Walker) circulation, could be a consequence of, and play an important role in determining, global warmth.” Michael W. Wara, Ana Christina Ravelo and Margaret L. Delaney, Science 29 July 2005: Vol. 309 no. 5735 pp. 758-761, DOI: 10.1126/science.1112596. [Full text]

Regional climate shifts caused by gradual global cooling in the Pliocene epoch – Ravelo et al. (2004) “The Earth’s climate has undergone a global transition over the past four million years, from warm conditions with global surface temperatures about 3 °C warmer than today, smaller ice sheets and higher sea levels to the current cooler conditions. Tectonic changes and their influence on ocean heat transport have been suggested as forcing factors for that transition, including the onset of significant Northern Hemisphere glaciation ~2.75 million years ago, but the ultimate causes for the climatic changes are still under debate. Here we compare climate records from high latitudes, subtropical regions and the tropics, indicating that the onset of large glacial/interglacial cycles did not coincide with a specific climate reorganization event at lower latitudes. The regional differences in the timing of cooling imply that global cooling was a gradual process, rather than the response to a single threshold or episodic event as previously suggested. We also find that high-latitude climate sensitivity to variations in solar heating increased gradually, culminating after cool tropical and subtropical upwelling conditions were established two million years ago. Our results suggest that mean low-latitude climate conditions can significantly influence global climate feedbacks.” Ana Christina Ravelo, Dyke H. Andreasen, Mitchell Lyle, Annette Olivarez Lyle & Michael W. Wara, Nature 429, 263-267 (20 May 2004) | doi:10.1038/nature02567. [Full text]

Role of tropics in changing the response to Milankovich forcing some three million years ago – Philander & Fedorov (2003) “Throughout the Cenozoic the Earth experienced global cooling that led to the appearance of continental glaciers in high northern latitudes around 3 Ma ago. At approximately the same time, cold surface waters first appeared in regions that today have intense oceanic upwelling: the eastern equatorial Pacific and the coastal zones of southwestern Africa and California. There was furthermore a significant change in the Earth’s response to Milankovich forcing: obliquity signals became large, but those associated with precession and eccentricity remained the same. The latter change in the Earth’s response can be explained by hypothesizing that the global cooling during the Cenozoic affected the thermal structure of the ocean; it caused a gradual shoaling of the thermocline. Around 3 Ma the thermocline was sufficiently shallow for the winds to bring cold water from below the thermocline to the surface in certain upwelling regions. This brought into play feedbacks involving ocean-atmosphere interactions of the type associated with El Niño and also mechanisms by which high-latitude surface conditions can influence the depth of the tropical thermocline. Those feedbacks and mechanisms can account for the amplification of the Earth’s response to periodic variations in obliquity (at a period of 41K) without altering the response to Milankovich forcing at periods of 100,000 and 23,000 years. This hypothesis is testable. If correct, then in the tropics and subtropics the response to obliquity variations is in phase with, and corresponds to, El Niño conditions when tilt is large and La Niña conditions when tilt is small.” Philander, S. G., and A. V. Fedorov (2003), Paleoceanography, 18(2), 1045, doi:10.1029/2002PA000837. [Full text]

Eocene (55-35 Ma)

El Niño in the Eocene greenhouse recorded by fossil bivalves and wood from Antarctica – Ivany et al. (2011) “Quasi-periodic variation in sea-surface temperature, precipitation, and sea-level pressure in the equatorial Pacific known as the El Niño – Southern Oscillation (ENSO) is an important mode of interannual variability in global climate. A collapse of the tropical Pacific onto a state resembling a so-called ‘permanent El Niño’, with a preferentially warmed eastern equatorial Pacific, flatter thermocline, and reduced interannual variability, in a warmer world is predicted by prevailing ENSO theory. If correct, future warming will be accompanied by a shift toward persistent conditions resembling El Niño years today, with major implications for global hydrological cycles and consequent impacts on socioeconomic and ecological systems. However, much uncertainty remains about how interannual variability will be affected. Here, we present multi-annual records of climate derived from growth increment widths in fossil bivalves and co-occurring driftwood from the Antarctic peninsula that demonstrate significant variability in the quasi-biennial and 3–6 year bands consistent with ENSO, despite early Eocene (∼50 Mya) greenhouse conditions with global average temperature ∼10 degrees higher than today. A coupled climate model suggests an ENSO signal and teleconnections to this region during the Eocene, much like today. The presence of ENSO variation during this markedly warmer interval argues for the persistence of robust interannual variability in our future greenhouse world.” Ivany, L. C., T. Brey, M. Huber, D. P. Buick, and B. R. Schöne (2011), Geophys. Res. Lett., 38, L16709, doi:10.1029/2011GL048635.

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Here is the new research published last week. I’m not including everything that was published but just some papers that got my attention. Those who follow my Facebook page (and/or Twitter) have already seen most of these, as I post these there as soon as they are published. Here, I’ll just put them out in one batch. Sometimes I might also point out to some other news as well, but the new research will be the focus here. Here’s the archive for the news of previous weeks. By the way, if this sort of thing interests you, be sure to check out A Few Things Illconsidered, they have a weekly posting containing lots of links to new research and other climate related news.

Published last week:

Antarctic sea ice trends are due to many factors

A multivariate analysis of Antarctic sea ice since 1979 – Neto et al. (2011) “Recent satellite observations have shown an increase in the total extent of Antarctic sea ice, during periods when the atmosphere and oceans tend to be warmer surrounding a significant part of the continent. Despite an increase in total sea ice, regional analyses depict negative trends in the Bellingshausen-Amundsen Sea and positive trends in the Ross Sea. Although several climate parameters are believed to drive the formation of Antarctic sea ice and the local atmosphere, a descriptive mechanism that could trigger such differences in trends are still unknown. In this study we employed a multivariate analysis in order to identify the response of the Antarctic sea ice with respect to commonly utilized climate forcings/parameters, as follows: (1) The global air surface temperature, (2) The global sea surface temperature, (3) The atmospheric CO2 concentration, (4) The South Annular Mode, (5) The Niño 3, (6) The Niño 3 + 4, 7) The Niño 4, (8) The Southern Oscillation Index, (9) The Multivariate ENSO Index, (10) the Total Solar Irradiance, (11) The maximum O3 depletion area, and (12) The minimum O3 concentration over Antarctica. Our results indicate that western Antarctic sea ice is simultaneously impacted by several parameters; and that the minimum, mean, and maximum sea ice extent may respond to a separate set of climatic/geochemical parameters.” Newton de Magalhães Neto, Heitor Evangelista, Kenny Tanizaki-Fonseca, Margareth Simões Penello Meirelles and Carlos Eiras Garcia, Climate Dynamics, DOI: 10.1007/s00382-011-1162-6.

Ozone over Iberian peninsula seems to be increasing

Long-Term Trends Of Total Ozone Column Over The Iberian Peninsula For The Period 1979-2008 – Antón et al. (2011) “The objective of this work is to analyze the total ozone column (TOC) trends over the Iberian Peninsula during the last 30 years (1979-2008). This study is carried out using TOC data derived from the Multi Sensor Reanalysis (MSR), Total Ozone Mapping Spectrometer (TOMS) and Global Ozone Monitoring Experiment (GOME). The analysis of the long-term ozone trends is focused on two sub-periods (1979-1994 and 1995-2008) in order to detect changes in the ozone trend pattern. The results show that the ozone depletion was statistically significant at the 95% confidence level during the first sub-period (1979-1994) in the entire region of study (except in the Southerner locations), with linear trends from -4.5 %/decade to -2.5 %/decade. These linear trends present a clear dependence on latitude, being higher for the Northerner locations than for the Southerner. By contrast, the analysis of the second sub-period of study (1995-2008) shows positive ozone trends over the Iberian Peninsula, with the highest values (+2.5 %/decade) in the Northeast of this region. This result indicates that the ozone layer may be responding as expected to the controls on ozone-depleting substances imposed by the Montreal Protocol. Additionally, a seasonal trend analysis is performed using the average of the deseasonalized monthly values for each season of the year. The seasonal analysis showed that the negative ozone trends during the first sub-period of study were statistically significant in the spring and winter, while that the seasonal ozone trends obtained during the second sub-period are positive but in general not significant at 95%.” M. Antón, D. Bortoli, P.S. Kulkarni, M.J. Costa, A.F. Domingues, D. Loyola, A.M. Silva and L. Alados-Arboledas, Atmospheric Environment, doi:10.1016/j.atmosenv.2011.08.058.

Great Plains of North America get some of their droughts from AMO

Key role of the Atlantic Multidecadal Oscillation in 20th century drought and wet periods over the Great Plains – Nigam et al. (2011) “The Great Plains of North America are susceptible to multi-year droughts, such as the 1930s ‘Dust Bowl’. The droughts have been linked to SST variability in the Pacific and Atlantic basins. This observationally rooted analysis shows the SST influence in multi-year droughts and wet episodes over the Great Plains to be significantly more extensive than previously indicated. The remarkable statistical reconstruction of the major hydroclimate episodes attests to the extent of the SST influence in nature, and facilitated evaluation of the basin contributions. We find the Atlantic SSTs to be especially influential in forcing multi-year droughts; often, more than the Pacific ones. The Atlantic Multidecadal Oscillation (AMO), in particular, contributed the most in two of the four reconstructed episodes (Dust Bowl Spring, 1980s fall wetness), accounting for almost half the precipitation signal in each case. The AMO influence on continental precipitation was provided circulation context from analysis of NOAA’s 20th Century Atmospheric Reanalysis. A hypothesis for how the AMO atmospheric circulation anomalies are generated from AMO SSTs is proposed to advance discussion of the influence pathways of the mid-to-high latitude SST anomalies. Our analysis suggests that the La Nina–US Drought paradigm, operative on interannual time scales, has been conferred excessive relevance on decadal time scales in the recent literature.” Nigam, S., B. Guan, and A. Ruiz-Barradas (2011), Geophys. Res. Lett., 38, L16713, doi:10.1029/2011GL048650.

Lake Chad – ex-giant lake

On the causes of the shrinking of Lake Chad – Gao et al. (2011) “Over the last 40 years, Lake Chad, once the sixth largest lake in the world, has decreased by more than 90% in area. In this study, we use a hydrological model coupled with a lake/wetland algorithm to simulate the effects of lake bathymetry, human water use, and decadal climate variability on the lake’s level, surface area, and water storage. In addition to the effects of persistent droughts and increasing irrigation withdrawals on the shrinking, we find that the lake’s unique bathymetry—which allows its division into two smaller lakes—has made it more vulnerable to water loss. Unfortunately the lake’s split is favored by the 1952–2006 climatology. Failure of the lake to remerge with renewed rainfall in the 1990s following the drought years of the 1970s and 1980s is a consequence of irrigation withdrawals. Under current climate and water use, a full recovery of the lake is unlikely without an inter-basin water transfer. Breaching the barrier separating the north and south lakes would reduce the amount of supplemental water needed for recovery.” H Gao et al 2011 Environ. Res. Lett. 6 034021 doi: 10.1088/1748-9326/6/3/034021. [Full text]

El Niño in the Eocene greenhouse recorded by fossil bivalves and wood from Antarctica – Ivany et al. (2011) “Quasi-periodic variation in sea-surface temperature, precipitation, and sea-level pressure in the equatorial Pacific known as the El Niño – Southern Oscillation (ENSO) is an important mode of interannual variability in global climate. A collapse of the tropical Pacific onto a state resembling a so-called ‘permanent El Niño’, with a preferentially warmed eastern equatorial Pacific, flatter thermocline, and reduced interannual variability, in a warmer world is predicted by prevailing ENSO theory. If correct, future warming will be accompanied by a shift toward persistent conditions resembling El Niño years today, with major implications for global hydrological cycles and consequent impacts on socioeconomic and ecological systems. However, much uncertainty remains about how interannual variability will be affected. Here, we present multi-annual records of climate derived from growth increment widths in fossil bivalves and co-occurring driftwood from the Antarctic peninsula that demonstrate significant variability in the quasi-biennial and 3–6 year bands consistent with ENSO, despite early Eocene (∼50 Mya) greenhouse conditions with global average temperature ∼10 degrees higher than today. A coupled climate model suggests an ENSO signal and teleconnections to this region during the Eocene, much like today. The presence of ENSO variation during this markedly warmer interval argues for the persistence of robust interannual variability in our future greenhouse world.” Ivany, L. C., T. Brey, M. Huber, D. P. Buick, and B. R. Schöne (2011), Geophys. Res. Lett., 38, L16709, doi:10.1029/2011GL048635.

Some coral reefs might be able to partially compensate for ocean acidification

Coral Reefs Modify Their Seawater Carbon Chemistry – Case Study from a Barrier Reef (Moorea, French Polynesia) – Kleypas et al. (2011) “Changes in the carbonate chemistry of coral reef waters is driven by carbon fluxes from two sources: concentrations of CO2 in the atmospheric and source water, and the primary production/respiration and calcification/dissolution of the benthic community. Recent model analyses have shown that, depending on the composition of the reef community, the air-sea flux of CO2 driven by benthic community processes can exceed that due to increases in atmospheric CO2 (ocean acidification). We field test this model and examine the role of three key members of benthic reef communities in modifying the chemistry of the ocean source water: corals, macroalgae and sand. Building on data from previous carbon flux studies along a reef-flat transect in Moorea (French Polynesia), we illustrate that the drawdown of total dissolved inorganic carbon (CT) due to photosynthesis and calcification of reef communities can exceed the draw down of total alkalinity (AT) due to calcification of corals and calcifying algae, leading to a net increase in aragonite saturation state (Ωa). We use the model to test how changes in atmospheric CO2 forcing and benthic community structure affect the overall calcification rates on the reef flat. Results show that between the preindustrial period and 1992, ocean acidification caused reef flat calcification rates to decline by an estimated 15%, but loss of coral cover caused calcification rates to decline by at least three times that amount. The results also show that the upstream-downstream patterns of carbonate chemistry were affected by the spatial patterns of benthic community structure. Changes in the ratio of photosynthesis to calcification can thus partially compensate for ocean acidification, at least on shallow reef flats. With no change in benthic community structure, however, ocean acidification depressed net calcification of the reef flat consistent with findings of previous studies.” Joan A. Kleypas, Kenneth R. N. Anthony, Jean-Pierre Gattuso, Global Change Biology, DOI: 10.1111/j.1365-2486.2011.02530.x.

Relation of extreme precipitation and surface temperature globally

Does higher surface temperature intensify extreme precipitation? – Utsumi et al. (2011) “Recently, against the backdrop of current climate, several regional studies have investigated the applicability of the Clausius–Clapeyron relation to the scaling relationship between extreme precipitation intensity and surface air temperature. Nevertheless, the temperature relationship of the extreme precipitation intensity on a global scale is still unclear. We assess, for the first time, the global relationship between the extreme daily precipitation intensity and the daily surface air temperature using in-situ data. The extreme daily precipitation intensity increased monotonically with the daily surface air temperature at high latitudes and decreased monotonically in the tropics. Similarly, the extreme daily precipitation intensity at middle latitudes increased at low temperatures and decreased at high temperatures; this decrease could be largely attributed to the decrease in the wet-event duration. The Clausius–Clapeyron scaling is applicable to the increase in the extreme daily precipitation intensity in a limited number of regions. However, the potential applicability of the Clausius–Clapeyron scaling on sub-hourly timescale was observed, even in regions where the Clausius–Clapeyron scaling on daily timescale was not applicable. This implies the potential of warming to intensify extreme precipitation on sub-hourly timescales.” Utsumi, N., S. Seto, S. Kanae, E. E. Maeda, and T. Oki (2011), Geophys. Res. Lett., 38, L16708, doi:10.1029/2011GL048426.

Earth’s surface energy has increased when all energy components are considered

Observed changes in surface atmospheric energy over land – Peterson et al. (2011) “The temperature of the surface atmosphere over land has been rising during recent decades. But surface temperature, or, more accurately, enthalpy which can be calculated from temperature, is only one component of the energy content of the surface atmosphere. The other parts include kinetic energy and latent heat. It has been advocated in certain quarters that ignoring these additional terms somehow calls into question global surface temperature analyses. Examination of all three of these components of atmospheric energetics reveals a significant increase in global surface atmospheric energy since the 1970s. Kinetic energy has decreased but by over two orders of magnitude less than the increases in both enthalpy and latent heat which provide approximately equal contributions to the global increases in heat content. Regionally, the enthalpy or the latent heat component can dominate the change in heat content. Although generally changes in latent heat and enthalpy act in concert, in some regions they can have the opposite signs.” Peterson, T. C., K. Willett, and P. W. Thorne (2011), Geophys. Res. Lett., doi:10.1029/2011GL048442.

TSI difference between recent minimum and Maunder mimimum is likely small

Are the most recent estimates for Maunder Minimum solar irradiance in agreement with temperature reconstructions? – Feulner (2011) “Estimates for the total solar irradiance (TSI) during the 17th-century Maunder Minimum published in the last few years have pointed towards a TSI difference of 0.2-0.7 W m−2 as compared to the 2008/2009 solar minimum. Two recent studies, however, give anomalies which differ from this emerging consensus. The first study indicates an even smaller TSI difference, placing the Maunder Minimum TSI on the same level as the 2008/2009 minimum. The second study on the other hand suggests a very large TSI difference of 5.8 W m−2. Here I use coupled climate simulations to assess the implications of these two estimates on Northern-hemisphere surface air temperatures over the past millennium. Using a solar forcing corresponding to the estimate of the first study, simulated Northern-hemisphere temperatures over the past millennium are consistent with reconstructed surface air temperatures. The large TSI differences between times of high and low solar activity as suggested by the second study, however, yield temperatures during all past grand solar minima that are too low, an excessive variance in Northern-hemisphere temperature on timescales of 50-100 years as compared to reconstructions, and temperatures during the first half of the 20th century which are too low and inconsistent with the instrumental temperature record. In summary this suggests a more moderate TSI difference of less than 1 W m−2 and possibly as low as 0-0.3 W m−2.” Feulner, G. (2011), Geophys. Res. Lett., doi:10.1029/2011GL048529.

New laboratory measurements of water vapor self-continuum IR-absorption

Water vapor self-continuum absorption in near-infrared windows derived from laboratory measurements – Ptashnik et al. (2011) “In most near-infrared atmospheric windows, absorption of solar radiation is dominated by the water vapor self-continuum and yet there is a paucity of measurements in these windows. We report new laboratory measurements of the self-continuum absorption at temperatures between 293 and 472 K and pressures from 0.015 to 5 atm in four near-infrared windows between 1 and 4 μm (10000-2500 cm-1); the measurements are made over a wider range of wavenumber, temperatures and pressures than any previous measurements. They show that the self-continuum in these windows is typically one order of magnitude stronger than given in representations of the continuum widely used in climate and weather prediction models. These results are also not consistent with current theories attributing the self-continuum within windows to the far-wings of strong spectral lines in the nearby water vapor absorption bands; we suggest that they are more consistent with water dimers being the major contributor to the continuum. The calculated global-average clear-sky atmospheric absorption of solar radiation is increased by ≈0.75 W/m2 (which is about 1% of the total clear-sky absorption) by using these new measurements as compared to calculations with the MT_CKD-2.5 self-continuum model.” Ptashnik, I. V., R. A. McPheat, K. P. Shine, K. M. Smith, and R. G. Williams (2011), J. Geophys. Res., doi:10.1029/2011JD015603.

Analysis of cloud radiative effect

Combining satellite data and models to estimate cloud radiative effect at the surface and in the atmosphere – Allan (2011) “Satellite measurements and numerical forecast model reanalysis data are used to compute an updated estimate of the cloud radiative effect on the global multi-annual mean radiative energy budget of the atmosphere and surface. The cloud radiative cooling effect through reflection of short wave radiation dominates over the long wave heating effect, resulting in a net cooling of the climate system of − 21 Wm−2. The short wave radiative effect of cloud is primarily manifest as a reduction in the solar radiation absorbed at the surface of − 53 Wm−2. Clouds impact long wave radiation by heating the moist tropical atmosphere (up to around 40 Wm−2 for global annual means) while enhancing the radiative cooling of the atmosphere over other regions, in particular higher latitudes and sub-tropical marine stratocumulus regimes. While clouds act to cool the climate system during the daytime, the cloud greenhouse effect heats the climate system at night. The influence of cloud radiative effect on determining cloud feedbacks and changes in the water cycle are discussed.” Richard P. Allan, Meteorological Applications, Volume 18, Issue 3, pages 324–333, September 2011, DOI: 10.1002/met.285.

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Here is the new research published last week. I’m not including everything that was published but just some papers that got my attention. Those who follow my Facebook page (and/or Twitter) have already seen most of these, as I post these there as soon as they are published. Here, I’ll just put them out in one batch. Sometimes I might also point out to some other news as well, but the new research will be the focus here. Here’s the archive for the news of previous weeks. By the way, if this sort of thing interests you, be sure to check out A Few Things Illconsidered, they have a weekly posting containing lots of links to new research and other climate related news. Planet 3.0 also reports new research.

Published last week:

Dune migration rate in Antarctica has increased with climate change

Is climate change affecting rates of dune migration in Antarctica? – Bristow et al. (2011) “Antarctica is the coldest, driest, and windiest continent on Earth, and contains sand dunes, like deserts elsewhere. The structure and age of the cold climate dunes found in the Victoria Valley, Antarctica, are described in the light of changing climate in the Ross Sea region of Antarctica during the late Holocene. Ground penetrating radar (GPR) was used to image sand dune stratigraphy, and optically stimulated luminescence (OSL) was used to determine when the sands were deposited. The timing of sand dune accretion identified from the GPR stratigraphy ranges from the present day to ca. 1.3 kyr B.P. The OSL ages were used to calculate end-point migration rates of 0.05–1.5 m/yr, lower than migration rates from photogrammetry and field surveys undertaken over the past 50 yr. The earliest recorded dune development, ca. 1.3 kyr B.P., was probably controlled by intensification of circumpolar westerlies at that time as well as by drier conditions and lower temperatures that promoted dune stabilization. The dune reactivation ca. 300 yr ago coincides with cooling ca. A.D. 1700–1850, and strengthening of southern circumpolar westerlies. The increase in rate of dune migration after this period and especially the past 200 yr may coincide with the modern rise in CO2 and the warmest temperatures in Antarctica during the past 800 kyr.” Charlie S. Bristow, Paul Augustinus, Ed J. Rhodes, Irene C. Wallis and Harry M. Jol, Geology, v. 39 no. 9 p. 831-834, doi: 10.1130/G32212.1. [Supplementary information]

Sea ice loss stays reversible says a model study

The reversibility of sea ice loss in a state-of-the-art climate model – Armour et al. (2011) “Rapid Arctic sea ice retreat has fueled speculation about the possibility of threshold (or ‘tipping point’) behavior and irreversible loss of the sea ice cover. We test sea ice reversibility within a state-of-the-art atmosphere–ocean global climate model by increasing atmospheric carbon dioxide until the Arctic Ocean becomes ice-free throughout the year and subsequently decreasing it until the initial ice cover returns. Evidence for irreversibility in the form of hysteresis outside the envelope of natural variability is explored for the loss of summer and winter ice in both hemispheres. We find no evidence of irreversibility or multiple ice-cover states over the full range of simulated sea ice conditions between the modern climate and that with an annually ice-free Arctic Ocean. Summer sea ice area recovers as hemispheric temperature cools along a trajectory that is indistinguishable from the trajectory of summer sea ice loss, while the recovery of winter ice area appears to be slowed due to the long response times of the ocean near the modern winter ice edge. The results are discussed in the context of previous studies that assess the plausibility of sea ice tipping points by other methods. The findings serve as evidence against the existence of threshold behavior in the summer or winter ice cover in either hemisphere.” Armour, K. C., I. Eisenman, E. Blanchard-Wrigglesworth, K. E. McCusker, and C. M. Bitz (2011), Geophys. Res. Lett., 38, L16705, doi:10.1029/2011GL048739. [Full text]

Thoroughly radiocarbon-dated 25000 year lake sediment record from East Africa

High-resolution 14C dating of a 25,000-year lake-sediment record from equatorial East Africa – Blaauw et al. (2011) “We dated a continuous, 22-m long sediment sequence from Lake Challa (Mt. Kilimanjaro area, Kenya/Tanzania) to produce a solid chronological framework for multi-proxy reconstructions of climate and environmental change in equatorial East Africa over the past 25,000 years. The age model is based on a total of 168 AMS 14C dates on bulk-organic matter, combined with a 210Pb chronology for recent sediments and corrected for a variable old-carbon age offset. This offset was estimated by i) pairing bulk-organic 14C dates with either 210Pb-derived time markers or 14C dates on grass charcoal, and ii) wiggle-matching high-density series of bulk-organic 14C dates. Variation in the old-carbon age offset through time is relatively modest, ranging from 450 yr during glacial and late glacial time to 200 yr during the early and mid-Holocene, and increasing again to 250 yr today. The screened and corrected 14C dates were calibrated sequentially, statistically constrained by their stratigraphical order. As a result their constrained calendar-age distributions are much narrower, and the calibrated dates more precise, than if each 14C date had been calibrated on its own. The smooth-spline age-depth model has 95% age uncertainty ranges of 50–230 yr during the Holocene and 250–550 yr in the glacial section of the record. The δ13C values of paired bulk-organic and grass-charcoal samples, and additional 14C dating on selected turbidite horizons, indicates that the old-carbon age offset in Lake Challa is caused by a variable contribution of old terrestrial organic matter eroded from soils, and controlled mainly by changes in vegetation cover within the crater basin.” Maarten Blaauw, Bas van Geel, Iris Kristen, Birgit Plessen, Anna Lyaruu, Daniel R. Engstrom, Johannes van der Plicht and Dirk Verschuren, Quaternary Science Reviews, doi:10.1016/j.quascirev.2011.07.014.

A review of sea level measurements and causes of change

Sea level and climate: measurements and causes of changes – Cazenave & Remy (2011) “We review present-day observations of sea level change and variability at global and regional scales, focusing on the altimetry era starting in the early 1990s. Over the past ∼18-years, the rate of global mean sea level rise has reached 3.3 ± 0.4 mm/year, nearly twice that of the previous decades, although the observed larger sea level rise rate may be influenced by decadal or longer variations in the ocean. Moreover, sea level rates are not geographically uniform; in some regions like the tropical western Pacific, rates are up to 3–4 times higher than the global mean rate. We next discuss the climate-related components of the global mean sea level rise. Over the last ∼18-years, ocean thermal expansion contributes about one third to the observed rise while total land ice (glacier melting plus ice sheet mass loss) contribute the other two third. The spatial trend patterns evidenced over the altimetry period mostly result from nonuniform steric sea level changes (effects of ocean temperature and salinity), largely caused by wind-driven ocean circulation changes. Such patterns are not stationary but oscillate through time on decadal/multidecadal time scale, in response to natural modes of the coupled ocean-atmosphere system. We close up this review by briefly discussing future (21st century) sea level rise. Current limited knowledge of the future evolution of the mass balance of the Greenland and Antarctica ice sheets leads to high uncertainty on the global mean sea level rise expected for the next 50–100 years.” Anny Cazenave, Frédérique Remy, Wiley Interdisciplinary Reviews: Climate Change, DOI: 10.1002/wcc.139.

New analysis of the recycling rate of atmospheric moisture

The recycling rate of atmospheric moisture over the past two decades (1988–2009) – Li et al. (2011) “Numerical models predict that the recycling rate of atmospheric moisture decreases with time at the global scale, in response to global warming. A recent observational study (Wentz et al 2007 Science 317 233–5) did not agree with the results from numerical models. Here, we examine the recycling rate by using the latest data sets for precipitation and water vapor, and suggest a consistent view of the global recycling rate of atmospheric moisture between numerical models and observations. Our analyses show that the recycling rate of atmospheric moisture has also decreased over the global oceans during the past two decades. In addition, we find different temporal variations of the recycling rate in different regions when exploring the spatial pattern of the recycling rate. In particular, the recycling rate has increased in the high-precipitation region around the equator (i.e., the intertropical convergence zone) and decreased in the low-precipitation region located either side of the equator over the past two decades. Further exploration suggests that the temporal variation of precipitation is stronger than that of water vapor, which results in the positive trend of the recycling rate in the high-precipitation region and the negative trend of the recycling rate in the low-precipitation region.” Liming Li et al 2011 Environ. Res. Lett. 6 034018 doi: 10.1088/1748-9326/6/3/034018. [Full text]

No clear cyclicity between Holocene cold and warm periods

Structure and origin of Holocene cold events – Wanner et al. (2011) “The present interglacial, the Holocene, spans the period of the last 11,700 years. It has sustained the growth and development of modern society. The millennial-scale decreasing solar insolation in the Northern Hemisphere summer lead to Northern Hemisphere cooling, a southern shift of the Intertropical Convergence Zone (ITCZ) and a weakening of the Northern Hemisphere summer monsoon systems. On the multidecadal to multicentury-scale, periods of more stable and warmer climate were interrupted by several cold relapses, at least in the Northern Hemisphere extra-tropical area. Based on carefully selected 10,000-year-long time series of temperature and humidity/precipitation, as well as reconstructions of glacier advances, the spatiotemporal pattern of six cold relapses during the last 10,000 years was analysed and presented in form of a Holocene Climate Atlas (HOCLAT; see http://www.oeschger.unibe.ch/research/projects/holocene_atlas/). A clear cyclicity was not found, and the spatiotemporal variability of temperature and humidity/precipitation during the six specific cold events (8200, 6300, 4700, 2700, 1550 and 550 years BP) was very high. Different dynamical processes such as meltwater flux into the North Atlantic, low solar activity, explosive volcanic eruptions, and fluctuations of the thermohaline circulation likely played a major role. In addition, internal dynamics in the North Atlantic and Pacific area (including their complex interaction) were likely involved.” Heinz Wanner, Olga Solomina, Martin Grosjean, Stefan P. Ritz and Markéta Jetel, Quaternary Science Reviews, doi:10.1016/j.quascirev.2011.07.010.

In Europe last decade was warmer than any time during MWP

A robust spatial reconstruction of April to September temperature in Europe: Comparisons between the Medieval period and the recent warming with a focus on extreme values – Guiot (2011) “This report presents a study of the variability in a recently published April to September gridded reconstruction temperatures in Europe and an analysis of their extremes. This reconstruction was based on tree rings, historical documents, pollen assemblages and ice cores. The methodology used, an original spectral analogue method, preserves long-term variations and the variability of temperature series, which guarantees the pertinence of the analysis of the extremes over a period as long as the last millennium. The analysis of the extremes was performed with the peak-over-threshold (POT) method over two warm periods (A.D. 1000-1350 and 1880-2007) and a cold period (A.D. 1350-1950). We found that (1) according to the long-term variations shown in this reconstruction, the growing season temperature during the last decade has exceeded all of those observed during the Medieval period; (2) the return period of the maximum event of the Medieval period has been reduced by at least a factor of 5; and (3) all decades before AD 1350 were warm on average but relatively heterogeneous, while the last decade was homogeneously warmer. A new result of this study concerning Europe is that this anthropogenic change is characterized by spatial homogeneity, with similar changes in both average temperatures and in the distribution of extreme events, while natural climate forcings induce warm periods with heterogeneous spatial patterns and less frequent extreme events.” Joël Guiot, Global and Planetary Change, doi:10.1016/j.gloplacha.2011.07.007.

Greenland glacier retreat now is more widespread than in early 20th century

Multi-decadal retreat of Greenland’s marine-terminating glaciers – Howat & Eddy (2011) “Many marine-terminating glaciers draining the Greenland ice sheet have retreated over the past decade, yet the extent and magnitude of retreat relative to past variability is unknown. We measure changes in front positions of 210 marine-terminating glaciers using Landsat imagery spanning nearly four decades and compare decadal-scale rates of change with earlier observations. We find that 90% of the observed glaciers retreated between 2000 and 2010, approaching 100% in the northwest, with rapid retreat observed in all sectors of the ice sheet. The current retreat is accelerating and likely began between 1992 and 2000, coincident with the onset of warming, following glacier stability and minor advance during a mid-century cooling period. While it is clear an extensive retreat occurred in the early 20th century, a period of increasing air temperatures, a comparison of our results with historical observations provides evidence that the current retreat is more widespread. The onset of rapid retreat with warming relative to the slow and lagged advance with cooling suggests an asymmetry in the response of marine fronts to external forcing.” Howat, Ian M., Eddy, Alex, Journal of Glaciology, Volume 57, Number 203, August 2011 , pp. 389-396(8). [Full text]

UHI not a major player in USA temperature trends

Climatic trends in major U.S. urban areas, 1950–2009 – Mishra & Lettenmaier (2011) “We evaluate changes in climatic indices for the 100 largest U.S. urban areas and paired surrounding non-urban areas. During the period 1950–2009, we find that there were statistically significant changes in as many as half of the urban areas in temperature-related indices, such as heating and cooling degree-days and number of warm and cool nights, almost all of which are reflective of a general warming. Similarly, statistically significant changes (mostly increases) in indices related to extreme precipitation, such as daily maximum intensities and number of days with heavy precipitation, were detected in as many of 30% of the urban areas. A paired analysis of urban and surrounding non-urban areas suggests that most temperature-related trends are attributable to regional climate change, rather than to local effects of urbanization, although the picture is more mixed for precipitation.” Mishra, V., and D. P. Lettenmaier (2011), Geophys. Res. Lett., 38, L16401, doi:10.1029/2011GL048255.

Global effect of Arctic sea ice-albedo feedback

Estimating the global radiative impact of the sea ice–albedo feedback in the Arctic – Hudson (2011) “A simple method for estimating the global radiative forcing caused by the sea ice–albedo feedback in the Arctic is presented. It is based on observations of cloud cover, sea ice concentration, and top-of-atmosphere broadband albedo. The method does not rely on any sort of climate model, making the assumptions and approximations clearly visible and understandable and allowing them to be easily changed. Results show that the globally and annually averaged radiative forcing caused by the observed loss of sea ice in the Arctic between 1979 and 2007 is approximately 0.1 W m−2; a complete removal of Arctic sea ice results in a forcing of about 0.7 W m−2, while a more realistic ice-free summer scenario (no ice for 1 month and decreased ice at all other times of the year) results in a forcing of about 0.3 W m−2, similar to present-day anthropogenic forcing caused by halocarbons. The potential for changes in cloud cover as a result of the changes in sea ice makes the evaluation of the actual forcing that may be realized quite uncertain since such changes could overwhelm the forcing caused by the sea ice loss itself, if the cloudiness increases in the summertime.” Hudson, S. R. (2011), J. Geophys. Res., 116, D16102, doi:10.1029/2011JD015804.

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Here is the new research published last week. I’m not including everything that was published but just some papers that got my attention. Those who follow my Facebook page (and/or Twitter) have already seen most of these, as I post these there as soon as they are published. Here, I’ll just put them out in one batch. Sometimes I might also point out to some other news as well, but the new research will be the focus here. Here’s the archive for the news of previous weeks. By the way, if this sort of thing interests you, be sure to check out A Few Things Illconsidered, they have a weekly posting containing lots of links to new research and other climate related news. Planet 3.0 also reports new research.

Published last week:

Evidence for strengthening of the atmospheric circulation over tropical Pacific

A Shift in Western Tropical Pacific Sea Level Trends during the 1990s – Merrifield (2011) “Pacific Ocean sea surface height trends from satellite altimeter observations for 1993–2009 are examined in the context of longer tide gauge records and wind stress patterns. The dominant regional trends are high rates in the western tropical Pacific and minimal to negative rates in the eastern Pacific, particularly off North America. Interannual sea level variations associated with El Niño–Southern Oscillation events do not account for these trends. In the western tropical Pacific, tide gauge records indicate that the recent high rates represent a significant trend increase in the early 1990s relative to the preceding 40 years. This sea level trend shift in the western Pacific corresponds to an intensification of the easterly trade winds across the tropical Pacific. The wind change appears to be distinct from climate variations centered in the North Pacific, such as the Pacific decadal oscillation. In the eastern Pacific, tide gauge records exhibit higher-amplitude decadal fluctuations than in the western tropical Pacific, and the recent negative sea level trends are indistinguishable from these fluctuations. The shifts in trade wind strength and western Pacific sea level rate resemble changes in dominant global modes of outgoing longwave radiation and sea surface temperature. It is speculated that the western Pacific sea level response indicates a general strengthening of the atmospheric circulation over the tropical Pacific since the early 1990s that has developed in concert with recent warming trends.” Merrifield, Mark A., 2011: A Shift in Western Tropical Pacific Sea Level Trends during the 1990s. J. Climate, 24, 4126–4138, doi: 10.1175/2011JCLI3932.1. [Full text]

Antarctic waters are warming

Multi-decadal warming and shoaling of Antarctic Intermediate Water – Schmidtko & Johnson (2011) “Antarctic Intermediate Water (AAIW) is a dominant Southern Hemisphere water mass that spreads from its formation regions just north of the Antarctic Circumpolar Current (ACC) to at least 20°S in all oceans. This study uses an isopycnal climatology constructed from Argo Conductivity-Temperature-Depth (CTD) profile data to define the current state of the AAIW salinity minimum (its core) and thence compute AAIW core pressure, potential temperature, salinity, and potential density anomalies since the mid-1970s from ship-based CTD profiles. The results are used to calculate maps of temporal property trends at the AAIW core, where statistically significant strong circumpolar shoaling (30–50 dbar decade−1), warming (0.05–0.15°C decade−1), and density reductions (up to −0.03 kg m−3 decade−1) are found. These trends are strongest just north of the ACC in the southeast Pacific and Atlantic oceans and decrease equatorward. Salinity trends are generally small, with their sign varying regionally. Bottle data are used to extend the AAIW core potential temperature anomaly analysis back to 1925 in the Atlantic, and ~1960 elsewhere. The modern warm AAIW core conditions appear largely unprecedented in the historical record: biennially and zonally binned median AAIW core potential temperatures within each ocean basin are, with the notable exception of the subtropical South Atlantic in the 1950s–70s, 0.2–1°C colder than modern values. Zonally averaged sea surface temperature anomalies around the AAIW formation latitudes in each ocean and sectoral Southern Annular Mode indices are used to put the AAIW core property trends and variations into context.” Sunke Schmidtko and Gregory C. Johnson, Journal of Climate 2011, doi: 10.1175/JCLI-D-11-00021.1. [Full text]

Analysis of snow cover changes in the Himalayan region

An analysis of snow cover changes in the Himalayan region using MODIS snow products and in-situ temperature data – Maskey et al. (2011) “Amidst growing concerns over the melting of the Himalayas’ snow and glaciers, we strive to answer some of the questions related to snow cover changes in the Himalayan region covering Nepal and its vicinity using Moderate Resolution Imaging Spectroradiometer (MODIS) snow cover products from 2000 to 2008 as well as in-situ temperature data from two high altitude stations and net radiation and wind speed data from one station. The analysis consists of trend analysis based on the Spearman’s rank correlation on monthly, seasonal and annual snow cover changes over five different elevation zones above 3,000 m. There are decreasing trends in January and in winter for three of the five elevation zones (all below 6,000 m), increasing trends in March for two elevation zones above 5,000 m and increasing trends in autumn for four of the five elevation zones (all above 4,000 m). Some of these observed trends, if continue, may result in changes in the spring and autumn season river flows in the region. Dominantly negative correlations are observed between the monthly snow cover and the in-situ temperature, net radiation and wind speed from the Pyramid station at 5,035 m (near Mount Everest). Similar correlations are also observed between the snow cover and the in-situ temperature from the Langtang station at 3,920 m elevation. These correlations explain some of the observed trends and substantiate the reliability of the MODIS snow cover products.” Shreedhar Maskey, Stefan Uhlenbrook and Sunal Ojha, Climatic Change, DOI: 10.1007/s10584-011-0181-y.

Borehole measurements show increasing temperatures in East Antarctica

Recent surface temperature trends in the interior of East Antarctica from borehole firn temperature measurements and geophysical inverse methods – Muto et al. (2011) “We use measured firn temperatures down to depths of 80 to 90 m at four locations in the interior of Dronning Maud Land, East Antarctica to derive surface temperature histories spanning the past few decades using two different inverse methods. We find that the mean surface temperatures near the ice divide (the highest-elevation ridge of East Antarctic Ice Sheet) have increased approximately 1 to 1.5 K within the past ∼50 years, although the onset and rate of this warming vary by site. Histories at two locations, NUS07-5 (78.65°S, 35.64°E) and NUS07-7 (82.07°S, 54.89°E), suggest that the majority of this warming took place in the past one or two decades. Slight cooling to no change was indicated at one location, NUS08-5 (82.63°S, 17.87°E), off the divide near the Recovery Lakes region. In the most recent decade, inversion results indicate both cooler and warmer periods at different sites due to high interannual variability and relatively high resolution of the inverted surface temperature histories. The overall results of our analysis fit a pattern of recent climate trends emerging from several sources of the Antarctic temperature reconstructions: there is a contrast in surface temperature trends possibly related to altitude in this part of East Antarctica.” Muto, A., T. A. Scambos, K. Steffen, A. G. Slater, and G. D. Clow (2011), Geophys. Res. Lett., 38, L15502, doi:10.1029/2011GL048086.

What happens to boreal soils under climate change?

Boreal and subarctic soils under climatic change – Helama et al. (2011) “Changing climate and warming atmosphere are supposed to result in changing thermal regimes of soils with a spectrum of impacts for terrestrial heat-flow, ecological and biochemical processes including vegetation and carbon dynamics. Here, six sites within an area of significant recent climatic warming, between 70° and 60°N, provided data of air and soil temperatures and snow depth to analyze the spatiotemporal air-soil temperature associations during the period 1971–2010. The air temperatures exhibited significant trends of warming across the boreal and subarctic region. The records of snow depth showed trends of snowpack thinning and the soil temperatures trends of warming especially in the southern and middle boreal sites. The boreal and subarctic sites showed predominant influence of air temperature variability on soil thermal conditions, with modulating effects of thermoinsulation caused by the snowpack. The yearly variations in soil temperatures correlated highly with those of air temperatures and the positive trend in soil temperatures was sufficiently explained by air temperature warming in the majority of the sites. The results thus propose that the climate change could be directly causing alterations in the soil thermal regime and the warming of soils, with generally expected continuation, driven by air temperature warming as projected by model simulations. The thermoinsulation effects during the winter were strongest in the northern boreal zone where the temperature difference between the air and soil temperatures was largest and the correlations between snow depth and soil temperatures were highest during the winter months. Likewise, the rate of air temperature warming appeared strongest in our northern boreal site where the soil temperature warming showed non-significant trend only. The evidence for temporal air-soil temperature decouplings and spatial disparity between the air and soil temperature data both expressed the importance of studying the soil temperature change in situ. In the same context, the potential for temperature induced soil organic carbon decomposition coincided spatially with the highest quantities of available carbon as indicated for our boreal and subarctic soils.” Samuli Helama, Heikki Tuomenvirta and Ari Venäläinen, Global and Planetary Change, doi:10.1016/j.gloplacha.2011.08.001.

Land-atmosphere coupling associated with snow cover – Dutra et al. (2011) “This study investigates the role of interannual snow cover variability in controlling the land-atmosphere coupling and its relation with near surface (T2M) and soil temperature (STL1). Global atmospheric simulations are carried out with the EC-EARTH climate model using climatological sea surface temperature and sea ice distributions. Snow climatology, derived from a control run (COUP), is used to replace snow evolution in the snow-uncoupled simulation (UNCOUP). The snow cover and depth variability explains almost 60% of the winter T2M variability in predominantly snow-covered regions. During spring the differences in interannual variability of T2M are more restricted to the snow line regions. The variability of soil temperature is also damped in UNCOUP. However, there are regions with a pronounced signal in STL1 with no counterpart in T2M. These regions are characterized by a significant interannual variability in snow depth, rather than snow cover (almost fully snow covered during winter). These results highlight the importance of both snow cover and snow depth in decoupling the soil temperature evolution from the overlying atmosphere.” Dutra, E., C. Schär, P. Viterbo, and P. M. A. Miranda (2011), Geophys. Res. Lett., 38, L15707, doi:10.1029/2011GL048435.

Large decadal decline of the Arctic multiyear ice

Large Decadal Decline of the Arctic Multiyear Ice Cover – Comiso (2011) “The perennial ice area was drastically reduced to 38% of its climatological average in 2007 but recovered slightly in 2008, 2009 and 2010 with the areas being 10%, 24%, and 11% higher than in 2007, respectively. However, trends in extent and area remained strongly negative at −12.2% and −13.5 %/decade, respectively. The thick component of the perennial ice, called multiyear ice, as detected by satellite data in the winters of 1979 to 2011 was studied and results reveal that the multiyear ice extent and area are declining at an even more rapid rate of −15.1% and −17.2 % per decade, respectively, with record low value in 2008 followed by higher values in 2009, 2010 and 2011. Such high rate in the decline of the thick component of the Arctic ice cover means a reduction in average ice thickness and an even more vulnerable perennial ice cover. The decline of the multiyear ice area from 2007 to 2008 was not as strong as that of the perennial ice area from 2006 to 2007 suggesting a strong role of second year ice melt in the latter. The sea ice cover is shown to be strongly correlated with surface temperature which is increasing at about three times global average in the Arctic but appears weakly correlated with the AO which controls the atmospheric circulation in the region. An 8 to 9-year cycle is apparent in the multiyear ice record which could explain in part the slight recovery in the last three years.” Josefino C. Comiso, Journal of Climate 2011, doi: 10.1175/JCLI-D-11-00113.1.

Analysis of fast draining lakes on the Greenland Ice Sheet

Fast draining lakes on the Greenland Ice Sheet – Selmes et al. (2011) “The rapid drainage of supraglacial lakes around the ablation zone of the Greenland Ice Sheet forms an important link between water at the surface and the ice sheet base, allowing surface meltwater to reach the bed and hence increase glacial velocity. The conduits formed by lake drainages may remain open during the remainder of the melt season providing a pathway for further meltwater to reach the base. We investigated the drainage behavior of lakes from all regions of the Greenland Ice Sheet for the period 2005–2009. We mapped the evolution of 2600 lakes from 3704 MODIS images detecting a mean of 263 drainage events per year, of which 61% occurred in the south-west region. Only 1% of lake drainages occurred in the rapidly thinning south-east region. Our results show marked differences between the hydrology of the different regions of the ice sheet, with few lake drainages occurring in the regions where the highest dynamic mass loss is occurring. In the south-west and north-east, lake drainages are common and could impact glacier dynamics; in the south-east they are rare and are thus unlikely to do so.” Selmes, N., T. Murray, and T. D. James (2011), Geophys. Res. Lett., 38, L15501, doi:10.1029/2011GL047872.

CO2 levels might not have been very high during Early Cretaceous

Early Cretaceous atmospheric pCO2 level recorded from pedogenic carbonates in China – Huang et al. (2011) “Pedogenic carbonates were collected from Early Cretaceous strata in Sichuan and Liaoning, China. These paleosol carbonates and calcareous paleosols were evaluated in order to reconstruct atmospheric CO2 concentrations during the Early Cretaceous using a paleosol barometer. Using the isotopic ratios of pedogenic carbonates from Early Cretaceous (early-middle Berriasian, early Valanginian) strata in Sichuan Basin, averaged atmospheric pCO2 is estimated to have been 360 ppmv in the early-middle Berriasian and a mean value of 241 ppmv in the early Valanginian. In the late Barremian in western Liaoning, however the average was 530 ppmv, with a range of 365 ppmv and 644 ppmv, lower than previous estimates of pCO2 for these time periods, consistent with the suggestion of overall climate cooling and paleotemperature fluctuation during the Early Cretaceous. This indicates that not all of the Cretaceous was a high or continuous CO2 greenhouse, especially during Early Cretaceous.” C.M. Huang, G.J. Retallack and C.S. Wang, Cretaceous Research, doi:10.1016/j.cretres.2011.08.001.

Cosmic ray contribution to global warming less than 8% since 1900

The contribution of cosmic rays to global warming – Sloan & Wolfendale (2011) “A search has been made for a contribution of the changing cosmic ray intensity to the global warming observed in the last century. The cosmic ray intensity shows a strong 11 year cycle due to solar modulation and the overall rate has decreased since 1900. These changes in cosmic ray intensity are compared to those of the mean global surface temperature to attempt to quantify any link between the two. It is shown that, if such a link exists, the changing cosmic ray intensity contributes less than 8% to the increase in the mean global surface temperature observed since 1900.” T. Sloan and A.W. Wolfendale, Journal of Atmospheric and Solar-Terrestrial Physics, doi:10.1016/j.jastp.2011.07.013. [Full text]

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This is a list of papers on global warming effects on tick populations and the diseases they spread. The list is not complete, and will most likely be updated in the future in order to make it more thorough and more representative.

Modelling the effects of recent changes in climate, host density and acaricide treatments on population dynamics of Ixodes ricinus in the UK – Dobson & Randolph (2011) “A population model for the tick Ixodes ricinus, the most significant vector of pathogens in Europe, is used to explore the relative impact of changes in climate, host density and acaricide-treated hosts on tick abundance and seasonality. A rise in temperature of the sort witnessed since 1989 speeds up the inter-stadial development of ticks, thereby reducing the cumulative effect of constant daily mortality rates and potentially raising population levels. The predicted earlier onset of tick-questing activity in the spring, due to stage-specific temperature thresholds, could increase contact between ticks and humans during recreational visits to the countryside in spring holidays. These tick population effects vary geographically with background climate. The significant increase in deer abundance across Europe, including the UK, in recent decades is predicted to drive tick population increases, the effect varying with the initial density of hosts. In areas only recently colonized by deer, tick numbers are predicted to rise dramatically (given suitable climatic conditions). Where host densities are already high, however, further increases may reduce numbers of questing ticks; unfed ticks leave the questing population more rapidly, even though the overall tick population (and therefore pathogen transmission potential) increases. Culling high-density deer populations as a control measure could, therefore, initially cause an apparent increase in questing ticks, with the predicted long-term population trajectory depending on the severity of the cull. Conversely, the further addition of large hosts (e.g. sheep) would effectively reduce the number of questing ticks and therefore the risk to humans. If such sheep were treated with acaricide, tick populations are predicted to decrease rapidly, to an extent that depends on the relative abundance of wild (untreated) and treated hosts. Tick control in designated areas may be achieved by using sheep in this way as ‘lethal mops’, as used to occur in the past when sheep were regularly dipped. Synthesis and applications: Both abiotic and biotic environmental changes witnessed recently could have contributed to apparent increases in tick populations, especially where these environmental factors were limiting in the past. The release of additional hosts treated with long-lasting acaricide is potentially an effective control strategy.” Andrew D. M. Dobson, Sarah E. Randolph, Journal of Applied Ecology, Volume 48, Issue 4, pages 1029–1037, August 2011, DOI: 10.1111/j.1365-2664.2011.02004.x.

Mathematical modelling of the impact of climatic conditions in France on Rhipicephalus sanguineus tick activity and density since 1960 – Beugnet et al. (2011) “Rhipicephalus sanguineus, the brown dog tick, has a worldwide distribution in areas with a relatively warm climate, including mild winters. This tick plays an important role as vector for various animal and human pathogens, including bacteria and protozoa. Based on precise daily meteorological data from the past 40 years, combined with mathematical modelling designed to predict tick activity, two modelling approaches were developed. The first examined the evolution of the number of weeks with favourable biological conditions for ticks in four French cities located at various latitudes of the country: Nîmes in the south, Paris in the north, Lyon in the east and Nantes in the west. The second analysed the extension of the geographical surface area in km(2) where the biological conditions favour tick activity for at least 12 weeks per year. Both analyses revealed clear evidence of increased temperatures coupled with an augmented tick activity index in three of the four cities. However, the change was not significant in Nîmes, where the climate is Mediterranean and the tick is already endemic. For Paris, Lyon and Nantes, the activity index values have increased significantly, i.e. by 4.4%, 4.0% and 3.4%, respectively. The distribution of the activity index values is evolving strongly with significantly fewer values below 50% since the 1960s and a clear decrease of values between 20% and 50% during the latest decade. Between 1960 and 2000, the theoretical extension of the surface area where the climatic index is suitable for R. sanguineus has increased by 66%. Even though several other important factors, such as changes in biotopes or human activity, are not included in this study, the resulting patterns and trends are noticeable. Our models constitute the first demonstration of the impact of climate change on the activity and distribution of ticks and confirm the observed northward migration trend for this Mediterranean domestic tick.” Beugnet F, Kolasinski M, Michelangeli PA, Vienne J, Loukos H., Geospat Health. 2011 May;5(2):255-63. [Full text]

Biology and ecology of the brown dog tick, Rhipicephalus sanguineus – Dantas-Torres (2010) “The brown dog tick (Rhipicephalus sanguineus) is the most widespread tick in the world and a well-recognized vector of many pathogens affecting dogs and occasionally humans. This tick can be found on dogs living in both urban and rural areas, being highly adapted to live within human dwellings and being active throughout the year not only in tropical and subtropical regions, but also in some temperate areas. Depending on factors such as climate and host availability, Rh. sanguineus can complete up to four generations per year. Recent studies have demonstrated that ticks exposed to high temperatures attach and feed on humans and rabbits more rapidly. This observation suggests that the risk of human parasitism by Rh. sanguineus could increase in areas experiencing warmer and/or longer summers, consequently increasing the risk of transmission of zoonotic agents (e.g., Rickettsia conorii and Rickettsia rickettsii). In the present article, some aspects of the biology and ecology of Rh. sanguineus ticks are discussed including the possible impact of current climate changes on populations of this tick around the world.” Filipe Dantas-Torres, Parasites & Vectors, Volume 3, Number 1, 26, DOI: 10.1186/1756-3305-3-26. [Full text]

To what extent has climate change contributed to the recent epidemiology of tick-borne diseases? – Randolph (2010) “There is no doubt that all vector-borne diseases are very sensitive to climatic conditions. Many such diseases have shown marked increases in both distribution and incidence during the past few decades, just as human-induced climate change is thought to have exceeded random fluctuations. This coincidence has led to the general perception that climate change has driven disease emergence, but climate change is the inevitable backdrop for all recent events, without implying causality. Coincidence and causality can be disentangled using tick-borne encephalitis (TBE) as a test case, based on the excellent long-term data for this medically significant European disease system. Detailed analysis of climate records since 1970 has revealed abrupt temperature increases just prior to the dramatic upsurge in TBE incidence in many parts of central and eastern Europe. Furthermore, the seasonal patterns of this temperature change are such as might have favoured the transmission of TBE virus between co-feeding ticks. Nevertheless, the pattern of climate change is too uniform to explain the marked heterogeneity in the timing and degree of TBE upsurge, for example in different counties within each of the Baltic countries. Recent decreases as well as increases in TBE incidence must also be taken into account. Instead of a single cause, a network of interacting factors, acting synergistically but with differential force in space and time, would generate this epidemiological heterogeneity. From analysis of past and present events, it appears that human behavioural factors have played a more significant role than purely biological enzootic factors, although there is an explicit causal linkage from one to the other. This includes a range of abiotic and biotic environmental factors, together with human behaviour determined by socio-economic conditions. Many of the abrupt changes followed from the shift from planned to market economies with the fall of Soviet rule. Comparisons between eight countries have indeed revealed a remarkable correlation between poverty indicators and the relative degree of upsurge in TBE from 1993. Against this background of longer-term shifts in TBE incidence, sudden spikes in incidence appear to be due to exceptional weather conditions affecting people’s behaviour, which have a differential impact depending on socio-economic factors. This new perspective may also help explain the epidemiology of Crimean-Congo haemorrhagic fever around the eastern Mediterranean region, including the current exceptional epidemic in Turkey.” Sarah E. Randolph, Veterinary Parasitology, Volume 167, Issues 2-4, 10 February 2010, Pages 92-94, doi:10.1016/j.vetpar.2009.09.011.

Altitudinal patterns of tick and host abundance: a potential role for climate change in regulating tick-borne diseases? – Gilbert (2010) “The impact of climate change on vector-borne infectious diseases is currently controversial. In Europe the primary arthropod vectors of zoonotic diseases are ticks, which transmit Borrelia burgdorferi sensu lato (the agent of Lyme disease), tick-borne encephalitis virus and louping ill virus between humans, livestock and wildlife. Ixodes ricinus ticks and reported tick-borne disease cases are currently increasing in the UK. Theories for this include climate change and increasing host abundance. This study aimed to test how I. ricinus tick abundance might be influenced by climate change in Scotland by using altitudinal gradients as a proxy, while also taking into account the effects of hosts, vegetation and weather effects. It was predicted that tick abundance would be higher at lower altitudes (i.e. warmer climates) and increase with host abundance. Surveys were conducted on nine hills in Scotland, all of open moorland habitat. Tick abundance was positively associated with deer abundance, but even after taking this into account, there was a strong negative association of ticks with altitude. This was probably a real climate effect, with temperature (and humidity, i.e. saturation deficit) most likely playing an important role. It could be inferred that ticks may become more abundant at higher altitudes in response to climate warming. This has potential implications for pathogen prevalence such as louping ill virus if tick numbers increase at elevations where competent transmission hosts (red grouse Lagopus lagopus scoticus and mountain hares Lepus timidus) occur in higher numbers.” Lucy Gilbert, Oecologia, Volume 162, Number 1, 217-225, DOI: 10.1007/s00442-009-1430-x.

Effects of Climate Change on Ticks and Tick-Borne Diseases in Europe – Gray et al. (2009) “Zoonotic tick-borne diseases are an increasing health burden in Europe and there is speculation that this is partly due to climate change affecting vector biology and disease transmission. Data on the vector tick Ixodes ricinus suggest that an extension of its northern and altitude range has been accompanied by an increased prevalence of tick-borne encephalitis. Climate change may also be partly responsible for the change in distribution of Dermacentor reticulatus. Increased winter activity of I. ricinus is probably due to warmer winters and a retrospective study suggests that hotter summers will change the dynamics and pattern of seasonal activity, resulting in the bulk of the tick population becoming active in the latter part of the year. Climate suitability models predict that eight important tick species are likely to establish more northern permanent populations in a climate-warming scenario. However, the complex ecology and epidemiology of such tick-borne diseases as Lyme borreliosis and tick-borne encephalitis make it difficult to implicate climate change as the main cause of their increasing prevalence. Climate change models are required that take account of the dynamic biological processes involved in vector abundance and pathogen transmission in order to predict future tick-borne disease scenarios.” J. S. Gray, H. Dautel, A. Estrada-Peña, O. Kahl, and E. Lindgren, Interdisciplinary Perspectives on Infectious DiseasesVolume 2009 (2009), Article ID 593232, 12 pages, doi:10.1155/2009/593232. [Full text]

Spatial distribution of Dermacentor reticulatus tick in Slovakia in the beginning of the 21st century – Bullová et al. (2009) “A new field survey monitoring the spatial distribution of Dermacentor (D.) reticulatus (Fabricius, 1794) tick in Slovakia was carried out in 2005–2008 in order to record changes in its distribution when compared to former studies. Last surveys on the geographical distribution were conducted in 1950s and 1970s and the presence of D. reticulatus was determined along the rivers in the south-east (Latorica) as well as in the south-west (Morava, Dunaj) Slovakia. In the present survey new areas with D. reticulatus occurrence were detected, providing evidence that this tick species has extended its range in the surroundings of its former habitats but also by at least 200 km further North and by 300 m of elevation into higher altitudes. D. reticulatus is known to transmit Babesia spp. causing babesiosis in cattle and dogs. Expansion of D. reticulatus range is therefore likely to bring a spread of babesiosis, which can be severe or fatal especially for dogs.” Eva Bullová, Martin Lukáň, Michal Stanko, Branislav Peťko, Veterinary Parasitology, Volume 165, Issues 3-4, 12 November 2009, Pages 357-360, doi:10.1016/j.vetpar.2009.07.023.

Emerging arthropod-borne diseases of companion animals in Europe – Beugnet & Marié (2009) “Vector-borne diseases are caused by parasites, bacteria or viruses transmitted by the bite of hematophagous arthropods (mainly ticks and mosquitoes). The past few years have seen the emergence of new diseases, or re-emergence of existing ones, usually with changes in their epidemiology (i.e. geographical distribution, prevalence, and pathogenicity). The frequency of some vector-borne diseases of pets is increasing in Europe, i.e. canine babesiosis, granulocytic anaplasmosis, canine monocytic ehrlichiosis, thrombocytic anaplasmosis, and leishmaniosis. Except for the last, these diseases are transmitted by ticks. Both the distribution and abundance of the three main tick species, Rhipicephalus sanguineus, Dermacentor reticulatus and Ixodes ricinus are changing. The conditions for such changes involve primarily human factors, such as travel with pets, changes in human habitats, social and leisure activities, but climate changes also have a direct impact on arthropod vectors (abundance, geographical distribution, and vectorial capacity). Besides the most known diseases, attention should be kept on tick-borne encephalitis, which seems to be increasing in western Europe, as well as flea-borne diseases like the flea-transmitted rickettsiosis. Here, after consideration of the main reasons for changes in tick vector ecology, an overview of each “emerging” vector-borne diseases of pets is presented.” Frederic Beugnet, Jean-Lou Marié, Veterinary Parasitology, Volume 163, Issue 4, 26 August 2009, Pages 298-305, doi:10.1016/j.vetpar.2009.03.028. [Full text]

Influence of some climatic factors on Ixodes ricinus ticks studied along altitudinal gradients in two geographic regions in Switzerland – Gern et al. (2008) “In the context of climate change, the seasonal activity of questing Ixodes ricinus and their infection with Borrelia burgdorferi sensu lato (s.l.) were examined in relation to some climatic data along altitudinal gradients in Switzerland. The first study took place in an Alpine area (Valais) from 750 to 1020 m above sea level. The other gradient was located on a mountain in the foothills of the Jura chain (Neuchâtel) from 620 to 1070 m above sea level. In the Alpine area, the highest questing tick density was observed at the highest altitude. At the lowest altitudes (750 and 880 m), very high saturation deficits, >10 mmHg, were present during most of the tick activity season and they seem to have impaired the thriving of tick populations. The second study in Neuchâtel (2003–2005) was a follow-up of a previous study (1999–2001) in which it was observed that tick density decreased with increasing altitude. During the follow-up study, substantial differences in questing tick density and phenology of ticks were observed: At high elevations, questing tick densities were 2.25 and 3.5 times higher for nymphs and adults, respectively, than during 1999–2001. As observed during 1999–2001, questing tick density decreased with increasing altitude in this site in 2003–2005. Tick questing density remained higher at the lowest altitude. Increased temperatures during summer months, more favorable for ticks, reaching values similar to those registered in the first study at the lowest elevations are probably responsible for the higher tick questing density at high altitudes. B. burgdorferi s.l. infection prevalence in ticks decreased with increasing altitudes along both altitudinal gradients. Long-lasting high saturation deficit values may limit the development of tick populations as too high a moisture stress has a negative effect on tick survival. This factor may have a permanent impact, as it is probably the case at the lowest altitudes in the Alpine area or a more transient effect like in the Neuchâtel gradient.” Lise Gern, Francisca Morán Cadenas, Caroline Burri, International Journal of Medical Microbiology, Volume 298, Supplement 1, 1 September 2008, Pages 55-59, doi:10.1016/j.ijmm.2008.01.005. [Full text]

Ixodes ricinus seasonal activity: Implications of global warming indicated by revisiting tick and weather data – Gray (2008) “A recent climate experiment predicted that average maximum summer temperatures in southern regions of the British Isles may approach 30 °C by the year 2020. An opportunity for retrospective analysis of the implications of such a change for tick phenology and disease transmission was presented by the coincidence of unusually high early summer temperatures in 1976 with the collection of tick data from sites in Ireland where host availability was controlled. Subsequent identification of diapause threshold periods and simulation of temperature-dependent tick development showed that high summer temperatures can cause mass transfer of ticks between development cohorts, resulting in increased activity and therefore increased disease transmission in late autumn and early spring. This suggests that in northern temperate regions of Europe global warming is likely to cause changes in the seasonal patterns of tick-borne diseases.” Jeremy S. Gray, International Journal of Medical Microbiology, Volume 298, Supplement 1, 1 September 2008, Pages 19-24, doi:10.1016/j.ijmm.2007.09.005.

Evidence for an increased geographical distribution of Dermacentor reticulatus in Germany and detection of Rickettsia sp. RpA4 – Dautel et al. (2006) “Two studies were performed to elucidate the current distribution of the tick Dermacentor reticulatus in Germany. In the first one in 2003, a total of 365 dogs from 171 sites in the states of Berlin and Brandenburg was screened for ticks, and the corresponding outdoor sites that the dogs usually visited were searched for host-seeking ticks by the flagging method. A total of 1155 ticks was removed from the dogs. The majority were Ixodes ricinus (88.5%), followed by D. reticulatus (9.1%) and I. hexagonus (2.4%). Altogether, 222 dogs carried I. ricinus (60.8%), 41 D. reticulatus (11.2%) and 15 I. hexagonus (4.1%) ticks. Based on scutal index determination, the removed I. ricinus and D. reticulatus had been feeding on the dogs for a mean of 4.0 and 4.5 days, respectively. The dogs infested with D. reticulatus lived at 26 different sites, all previously unknown as Dermacentor sites. Seven of the sites could be confirmed subsequently by flagging the vegetation for ticks. In the second study, a total of 721 deer was shot at 201 different sites from a total of 160 districts all over Germany during the autumn hunting season 2004. A total of 23 deer (3.2%) originating from 14 sites was infested with D. reticulatus. Hereby, significantly more red deer (Cervus elaphus elaphus) than roe deer (Capreolus capreolus) or fallow deer (Dama dama) harboured D. reticulatus ticks. Only two of the sites found had already been known as D. reticulatus areas, whereas all other sites in Brandenburg, Saxony Anhalt, Hesse and Bavaria had been unknown. The results of both studies show that D. reticulatus presently occurs at far more sites than previously known in Germany and thus most likely has expanded its range. Additionally, a total of 135 D. reticulatus removed from deer was screened for Babesia canis and Rickettsia sp. by PCR. A total of 31 D. reticulatus (23%) were positive for Rickettsia. Sequencing revealed in all cases 100% identity with the strain RpA4 that was first isolated from Rhipicephalus ticks in Russia.” Hans Dautel, Cornelia Dippel, Rainer Oehme, Kathrin Hartelt, Elvira Schettler, International Journal of Medical Microbiology, Volume 296, Supplement 1, 22 May 2006, Pages 149-156, doi:10.1016/j.ijmm.2006.01.013.

A dynamic population model to investigate effects of climate on geographic range and seasonality of the tick Ixodes scapularis – Ogden et al. (2005) “A dynamic population model of Ixodes scapularis, the vector of a number of tick-borne zoonoses in North America, was developed to simulate effects of temperature on tick survival and seasonality. Tick development rates were modelled as temperature-dependent time delays, calculated using mean monthly normal temperature data from specific meteorological stations. Temperature also influenced host-finding success in the model. Using data from stations near endemic populations of I. scapularis, the model reached repeatable, stable, cyclical equilibria with seasonal activity of different instars being very close to that observed in the field. In simulations run using data from meteorological stations in central and eastern Canada, the maximum equilibrium numbers of ticks declined the further north was the station location, and simulated populations died out at more northerly stations. Tick die-out at northern latitudes was due to a steady increase in mortality of all life stages with decreasing temperature rather than a specific threshold event in phenology of one life stage. By linear regression we investigated mean annual numbers of degree-days >0 °C (DD>0 °C) as a readily mapped index of the temperature conditions at the meteorological stations providing temperature data for the model. Maximum numbers of ticks at equilibrium were strongly associated with the mean DD>0 °C (r2>0.96, POntario, β=103, P<0.001). The intercepts of the regression models provided theoretical limits for the establishment of I. scapularis in Canada. Maps of these limits suggested that the range of southeast Canada where temperature conditions are currently suitable for the tick, is much wider than the existing distribution of I. scapularis, implying that there is potential for spread. Future applications of the model in investigating climate change effects on I. scapularis are discussed." N.H. Ogden, M. Bigras-Poulin, C.J. O’Callaghan, I.K. Barker, L.R. Lindsay, A. Maarouf, K.E. Smoyer-Tomic, D. Waltner-Toews and D. Charron, International Journal for Parasitology, Volume 35, Issue 4, 1 April 2005, Pages 375-389, doi:10.1016/j.ijpara.2004.12.013. [Full text]

Evidence that climate change has caused ‘emergence’ of tick-borne diseases in Europe? – Randolph (2004) “Even though tick-borne disease systems are highly susceptible to climatic influences, climate change to date is not necessarily the cause of the marked increased incidence of a variety of tick-borne diseases in many parts of Europe over the past two decades. To test for causality, rather than coincidence, we need to examine whether the right sorts of climate change have occurred at the right time and in the right places to account for the observed heterogeneous temporal and spatial patterns of tick-borne disease ‘emergence’. Tick-borne encephalitis (TBE) incidence, for example, showed a 3-fold step increase from 1983 to 1986 in Sweden, doubled in 1993 in the Czech Republic, increased even more dramatically in the same year in Lithuania and Poland, but declined markedly in 1997 in Hungary, Croatia and Slovenia. Within each country, TBE incidence has changed to different degrees in different regions. Because other tick-borne diseases, notably Lyme borreliosis, has commonly ‘emerged’ in parallel with TBE, we should first examine climate variables predicted to have a general effect on tick abundance, which has indeed increased in the past decade. These include temperature and moisture stress, which have seasonally differential impacts. Monthly mean records for 1960–2000 from the UK Climate Research Unit’s interpolated global climate surface reveal that mean spring, spring-autumn and winter temperatures have all increased gradually over the past 40 years, but apparently most sharply in the late 1980s, when moisture stress also increased. These climate data do not reveal any obvious differences between sites where TBE did or did not ‘emerge’, and in Sweden increases in TBE pre-dated the onset of warmer springs and winters. If recorded climate changes cannot yet satisfactorily explain the temporal and spatial patterns of tick-borne disease change in Europe, the impact of biotic factors, such as increases in deer abundance and changing habitat structure, and of socio-political changes following the end of communist rule, demand more detailed quantitative analyses.” Sarah E. Randolph, International Journal of Medical Microbiology Supplements, Volume 293, Supplement 37, April 2004, Pages 5-15, doi:10.1016/S1433-1128(04)80004-4.

A tick-borne encephalitis ceiling in Central Europe has moved upwards during the last 30 years: Possible impact of global warming? – Zeman & Beneš (2004) “The geographic/temporal pattern of cases of tick-borne encephalitis (TBE) registered in the Czech Republic since 1970 was analysed to verify the surmise of a global warming effect. Using a geographic information system, over 8,700 notified places of infection were pinpointed on a map and overlaid with a digital elevation model to estimate the vertical distribution of the cases. Series of yearly disease ceilings (assessed alternatively as the respective maximum altitude or mean altitudes of the upper 5 or 10 cases) were tested against the null hypothesis of random elevation course and analysed for correlation with concomitant factors (yearly TBE incidence rate, mean yearly temperature, population density of small rodents and roe deer). Statistical tests proved that the TBE ceiling has gradually moved upwards in the course of the last three decades. The average rate of ascension within this period was approx. 5.4 ± 1.7 m yearly, which corresponds well with concurrent mean temperature rising of approx. 0.036 ± 0.007°C yearly, and the vertical temperature gradient of 0.0065 ± 0.0004°C m−1. The TBE-ceiling estimates significantly correlated with TBE-incidence data and the mean yearly temperature recorded 1–2 years earlier. Although TBE incidence correlated with rodent population density that was observed 1–2 years earlier, the TBE ceiling does not seem to be influenced by rodent population dynamics nor did the population dynamics correlate with mean yearly temperatures. TBE incidence as well as mean altitudes of the upper 10 cases also correlated with official data on harvested roe deer. Overall, the fluctuations of TBE incidence and TBE ceiling proved to be synchronous processes that correspond with temperature changes. Although the dependence of TBE on temperature is not a direct one and various factors could be involved, an impact of climate warming on the vertical disease distribution in Central Europe is evident.” Petr Zemana and Cestmir Beneš, International Journal of Medical Microbiology Supplements, Volume 293, Supplement 37, April 2004, Pages 48-54, doi:10.1016/S1433-1128(04)80008-1.

Tick-borne encephalitis in Sweden and climate change – Lindgren & Gustafson (2001) “Background: The incidence of tick-borne encephalitis (TBE) in Sweden has substantially increased since the mid-1980s. During the same period the climate has become milder and ticks have become more abundant. We investigated whether there is a link between the change in climate and the increase in incidence of TBE. Methods: Since the late 1950s all cases of encephalitis admitted in Stockholm County have been serologically tested for TBE. We analysed the period 1960–98 with multiple regressions. The number of days per season with temperatures of known importance for tick prevalence and pathogen transmission were studied. 2 years of temperature data were related to each TBE incidence rate to account for the tick’s long life-span. Findings: Increases in disease incidence was significantly related (R2=0·58; p<0·0001) to a combination of two consecutive mild winters, temperatures favouring spring development (8–10°C) and extended autumn activity (5–8°C) in the year prior to the incidence year, and temperatures allowing tick activity (5–8°C) early in the incidence year. Interpretations: The findings indicate that the increase in TBE incidence since the mid-1980s is related to the period's change towards milder winters and early arrival of spring. Other factors may have influenced TBE incidence such as more people in endemic locations, and increases in host animal populations; factors which are partly climate related. Access to TBE vaccination since 1986 and increased awareness of ticks might have caused an underestimation of the links found. Our findings also suggest that the incidence of other tick-borne zoonoses might have been affected by the milder climate." Elisabet Lindgren and Rolf Gustafson, The Lancet, Volume 358, Issue 9275, 7 July 2001, Pages 16-18, doi:10.1016/S0140-6736(00)05250-8. [Full text]

Fragile transmission cycles of tick-borne encephalitis virus may be disrupted by predicted climate change – Randolph & Rogers (2000) “Repeated predictions that vector–borne disease prevalence will increase with global warming are usually based on univariate models. Toaccommodate the full range of constraints, the present–day distribution of tick–borne encephalitis virus (TBEv) was matched statistically to current climatic variables, to provide a multivariate description of present–day areas of disease risk. This was then applied to outputs of a general circulation model that predicts how climatic variables may change in the future, and future distributions of TBEv were predicted for them. The expected summer rise in temperature and decrease in moisture appears to drive the distribution of TBEv into higher–latitude and higher–altitude regions progressively through the 2020s, 2050s and 2080s. The final toe–hold in the 2080s may be confined to a small part of Scandinavia, including new foci in southern Finland. The reason for this apparent contraction of the range of TBEv is that its transmission cycles depend on a particular pattern of tick seasonal dynamics, which may be disrupted by climate change. The observed marked increase in incidence of tick–borne encephalitis in most parts of Europe since 1993 may be due to non–biological causes, such as political and sociological changes.” Sarah E. Randolph and David J. Rogers, Proc. R. Soc. Lond. B 7 September 2000 vol. 267 no. 1454 1741-1744, doi: 10.1098/rspb.2000.1204. [Full text]

Impact of climatic change on the northern latitude limit and population density of the disease-transmitting European tick Ixodes ricinus – Lindgren et al. (2000) “We examined whether a reported northward expansion of the geographic distribution limit of the disease-transmitting tick Ixodes ricinus and an increased tick density between the early 1980s and mid-1990s in Sweden was related to climatic changes. The annual number of days with minimum temperatures above vital bioclimatic thresholds for the tick’s life-cycle dynamics were related to tick density in both the early 1980s and the mid-1990s in 20 districts in central and northern Sweden. The winters were markedly milder in all of the study areas in the 1990s as compared to the 1980s. Our results indicate that the reported northern shift in the distribution limit of ticks is related to fewer days during the winter seasons with low minimum temperatures, i.e., below -12 degrees C. At high latitudes, low winter temperatures had the clearest impact on tick distribution. Further south, a combination of mild winters (fewer days with minimum temperatures below -7 degrees C) and extended spring and autumn seasons (more days with minimum temperatures from 5 to 8 degrees C) was related to increases in tick density. We conclude that the relatively mild climate of the 1990s in Sweden is probably one of the primary reasons for the observed increase of density and geographic range of I. ricinus ticks.” E Lindgren, L Tälleklint, and T Polfeldt, Environ Health Perspect. 2000 February; 108(2): 119–123. [Full text]

Seasonal synchrony: the key to tick-borne encephalitis foci identified by satellite data – Randolph et al. (2000) “A previous analysis of tick infestation patterns on rodents in Slovakia suggested that the key to the focal distribution of western-type tick-borne encephalitis virus (TBEv) in Europe is the geographically variable degree of synchrony in the seasonal activity of larval and nymphal Ixodes ricinus ticks. This prediction is here tested by examining records, from 7 different countries, of the seasonal variation in the abundance of larvae and nymphs feeding on rodents or questing on the vegetation. Larvae consistently started feeding and questing earlier in the year at sites within TBEv foci than elsewhere, so that they appeared in the spring as soon as nymphs were active. Such larval–nymphal synchrony is associated with a rapid fall in ground-level temperatures from August to October as revealed by the satellite-derived index of Land Surface Temperature (LST). Likewise, of 1992 pixels sampled on a grid across Europe, the 418 that fell within TBEv foci were characterized by a higher than average rate of autumnal cooling relative to the peak midsummer LST. It is proposed that such a seasonal temperature profile may cause unfed larvae to pass the winter in quiescence, from which they emerge synchronously with nymphs in the spring.” S. E. Randolph, R. M. Green, M. F. Peacey and D. J. Rogers, Parasitology, 2000, 121: 15-23. [Full text]

Ticks and tick-borne disease systems in space and from space – Randolph (2000) “Analyses within geographical information systems (GISs) indicate that small- and large-scale ranges of hard tick species (Ixodidae) are determined more by climate and vegetation than by host-related factors. Spatial distributions of ticks may therefore be analysed by statistical methods that seek correlations between known tick presence/absence and ground- or remotely-sensed (RS) environmental factors. In this way, local habitats of Amblyomma variegatum in the Caribbean and Ixodes ricinus in Europe have been mapped using Landsat RS imagery, while regional and continental distributions of African and temperate tick species have been predicted using multi-temporal information from the National Oceanic and Atmospheric Administration-Advanced Very High Resolution Radiometer (NOAA-AVHRR) imagery. These studies illustrate ways of maximizing statistical accuracy, whose interpretation is then discussed in a biological framework. Methods such as discriminant analysis are biologically transparent and interpretable, while others, such as logistic regression and tree-based classifications, are less so. Furthermore, the most consistently significant variable for predicting tick distributions, the RS Normalized Difference Vegetation Index (NDVI), has a sound biological basis in that it is related to moisture availability to free-living ticks and correlated with tick mortality rates. The development of biological process-based models for predicting the spatial dynamics of ticks is a top priority, especially as the risk of tick-borne infections is commonly related not simply to the vector’s density, but to its seasonal population dynamics. Nevertheless, using statistical pattern-matching, the combination of RS temperature indices and NDVI successfully predicts certain temporal features essential for the transmission of tick-borne encephalitis virus, which translate into a spatial pattern of disease foci on a continental scale.” S.E. Randolph, Advances in Parasitology, Volume 47, 2000, Pages 217-243, Remote Sensing and Geographical Information Systems in Epidemiology, doi:10.1016/S0065-308X(00)47010-7.

Climate and Tickborne Encephalitis – Lindgren (2000) “Climatic changes are projected to alter the abundance, dynamics, and geographical distribution of many vector-borne diseases in human populations. Tick-borne diseases such as Lyme disease and tick-borne encephalitis (TBE) are a growing concern in northern Europe and the United States. The impact of a future climate change on the transmission of tick-borne diseases is not known. To make such assumptions, more empirical data are needed on the relations between short-term fluctuations in contemporary weather and disease incidence. This paper analyzes relations between daily minimum and maximum temperatures, monthly precipitation, and TBE incidence during a 36-yr period in Stockholm County, a high-endemic region for TBE in Sweden. Multiple regression analyses were performed, with temperature variables expressed as number of days per winter or spring – summer – fall season with temperatures above, below, or in the interval between different temperature limits. The limits used for daily minimum temperatures represent bioclimatic thresholds of importance for pathogen transmission. To adjust for the length of the tick’s life cycle, each TBE incidence rate was related to meteorological data over two consecutive years. Results reveal that increased incidence of tick-borne encephalitis is related to a combination of two successive years of more days with temperatures permitting prolonged seasonal tick activity and, hence, pathogen transmission (i.e., daily minimum temperatures above 5ºC-10ºC), and a mild winter preceding the year before the incidence year (i.e., fewer winter days with minimum temperatures below -7ºC). Alternative explanations of the results are discussed. Findings of this study suggest that a climate change may extend the seasonal range and intensify the endemicity of tick-borne diseases, in particular, at northern latitudes.” Elisabet Lindgren. 1998, Conservation Ecology [online] 2(1): 5.. [Full text]

Climate change, tick-borne encephalitis and vaccination needs in Sweden—a prediction model – Lindgren (1998) “A future, global, climate change may indirectly lead to changes in the transmission and incidence of several vector-borne diseases. This paper presents an example of a modeling tool for projections of possible changes in the incidence of tick-borne encephalitis (TBE), and the subsequent changes in vaccination needs, during the next half-century in Sweden. The model is based on the Hadley Center’s regional temperature predictions for the year 2050, taking into account the IPCC IS92 ‘non-intervention scenario’. The model has been constructed into STELLA, a graphical dynamic-simulation, soft-ware program. The model project an increase in TBE incidence in Stockholm County, a high-endemic region in Sweden, during the next 50 years. According to this simplified model, the annual vaccination rate need to increase by 3–4-fold during the next half century in order to prevent the projected increases in TBE incidence in the region from a climatic change.” Elisabet Lindgren, Ecological Modelling, Volume 110, Issue 1, 1 July 1998, Pages 55-63, doi:10.1016/S0304-3800(98)00041-6. [Full text]

Increasing Geographical Distribution and Density of Ixodes ricinus (Acari: Ixodidae) in Central and Northern Sweden – Tälleklint & Jaenson (1998) “The geographical distribution and density of Ixodes ricinus (L.) in the 2 northern regions, Svealand and Norrland, in Sweden were studied by using a questionnaire in Swedish magazines for house owners and dog owners, and in provincial newspapers. Analysis of the ≍1,200 answers revealed that ticks are present in all parts of Svealand (except northern Varmland and northern and western Dalarna), the southeastern part of Norrland (i.e., Gästrikland and Hälsingland), and along the Baltic Sea coast of central and northern Norrland. The proportion of answers reporting ticks and the estimated tick density (i.e., the number of ticks infesting dogs and cats) decreased from south to north. The answers to the questionnaire and data from field sampling of ticks suggest that tick density decreased distinctly along a narrow boundary zone, coinciding with the biological limit of Norrland (Limes Norrlandicus), crossing Sweden through southern Varmland, southeastern Dalarna, and central Gastrikland. The results of the questionnaire suggest that I. ricinus ticks are more widespread today than in the early 1980s, especially in Varmland, western and central Dalarna, Hiilsingland, and the coastal areas of Medelpad, Angermanland, and Vasterbotten, and that the proportion of the human population at risk for tick-borne pathogens in Svealand and Norrland is increasing.” Tälleklint, Lars; Jaenson, Thomas G. T., Journal of Medical Entomology, Volume 35, Number 4, July 1998 , pp. 521-526(6).

Geographical Distribution, Host Associations, and Vector Roles of Ticks (Acari: Ixodidae, Argasidae) in Sweden – Jaenson et al. (1994) “This review covers the geographic distribution and host relationships of the tick species in Sweden. Ixodes uriae White, I. caledonicus Nuttall, I. unicavatus Neumann, I. arboricola Schulze & Schlottke, and I. lividus Koch are ornithophagous species. I. trianguliceps Birula, I. canisuga Johnston, I. hexagonus Leach, and Argas vespertilionis (Latreille) are mammalophagous. I. ricinus (L.) and Haemaphysails punctata Canestrini & Fanzago feed on both birds and mammals. All these tick species may be considered to be permanently present in Sweden. I. persulcatus Schulze, Hyalomma marginatum Koch, and the brown dog tick, Rhipicephalus satiguineus (Latreille), may be regarded as not indigenous to Sweden although they may be regularly introduced by spring-migrating birds or imported dogs, respectively. The first European record of the American dog tick, Dermacentor variabilis (Say), is reported. There are several records of Hyalomma aegyptium (L.) from imported tortoises in Sweden. Excluding other ticks imported on exotic pets and zoo animals, another 13 tick species are listed that may occur, at least occasionally, in Sweden. Because of its wide geographic distribution, great abundance, and wide host range, I. ricinus is medically the most important arthropod in northern Europe. I. ricinus is common in southern and south-central Sweden and along the coast of northern Sweden and has been recorded from 29 mammal species, 56 bird species, and two species of lizards in Sweden alone. The potential introduction to Sweden of exotic pathogens with infected ticks (e.g., I. persulcatus and H. marginatum on birds or Dermacentor spp. and R. sanguineus on mammals) is evident.” Jaenson, Thomas G. T., Tälleklint, Lars, Lundqvist, Lars, Olsen, Björn, Chirico, Jan, Mejlon, Hans, Journal of Medical Entomology, Volume 31, Number 2, March 1994 , pp. 240-256(17).

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Here is the new research published last week. I’m not including everything that was published but just some papers that got my attention. Those who follow my Facebook page (and/or Twitter) have already seen most of these, as I post these there as soon as they are published. Here, I’ll just put them out in one batch. Sometimes I might also point out to some other news as well, but the new research will be the focus here. Here’s the archive for the news of previous weeks. By the way, if this sort of thing interests you, be sure to check out A Few Things Illconsidered, they have a weekly posting containing lots of links to new research and other climate related news. Planet 3.0 also reports new research.

Published last week:

Clouds are too reflective in many models in tropical convection regions

Reproducibility by climate models of cloud radiative forcing associated with tropical convection – Ichikawa et al. (2011) “In this study, cloud radiative forcing (CRF) associated with convective activity over tropical oceans is analyzed for monthly mean data of the twentieth-century simulations of 18 climate models participating in the phase 3 of the Coupled Model Intercomparison Project (CMIP3) in comparison with observational and reanalysis data. The analysis is focused on the warm oceanic regions with sea surface temperatures (SSTs) above 27°C to exclude the regions with cold SSTs typically covered by low stratus clouds. CRF is evaluated for different regimes sorted by pressure-coordinated vertical motion at 500 hPa (ω 500) as an index of large-scale circulation. The warm oceanic regions cover the regime of vertical motion ranging from strong ascent to weak descent. The most notable feature found in this study is a systematic underestimation by most models of the ratio of longwave cloud radiative forcing (LWCRF) to shortwave cloud radiative forcing (SWCRF) over the weak vertical motion regime defined as −10 < ω 500 < 20 hPa day−1. The underestimation of the ratio corresponds to the underestimation of LWCRF and the overestimation of SWCRF. Clouds in models seem to be lower in amount of high clouds but more reflective than those in the observation in this regime. In the weak vertical motion regime, the lower free troposphere is dry. In the large-scale environment condition, the reproducibility of LWCRF is high in models adopting the scheme where the relative humidity-based suppression for deep convection occurrence is implemented. Models adopting Zhang and McFarlane scheme show good performance without such a suppression mechanism." Hiroki Ichikawa, Hirohiko Masunaga, Yoko Tsushima, and Hiroshi Kanzawa, Journal of Climate 2011, doi: 10.1175/JCLI-D-11-00114.1.

Adult exposure influences offspring response to ocean acidification in oysters – Parker et al. (2011) “It is essential to predict the impact of elevated Pco2 on marine organisms and habitats in order to anticipate the severity and consequences of future ocean chemistry change. Despite the importance of carry-over effects in the evolutionary history of marine organisms, few studies have considered links between life-history stages when determining how marine organisms will respond to elevated Pco2, and none have considered the link between adults and their offspring. Here we exposed adults of wild and selectively bred Sydney rock oysters, Saccostrea glomerata to elevated Pco2 during reproductive conditioning and measured the development, growth and survival response of their larvae. We found that elevated Pco2 had a negative impact on larvae of S. glomerata causing a reduction in growth, rate of development and survival. Exposing adults to elevated Pco2 during reproductive conditioning, however, had positive carry-over effects on larvae. Larvae spawned from adults exposed to elevated Pco2 were larger, developed faster but displayed similar survival compared to larvae spawned from adults exposed to ambient Pco2. Further, selectively bred larvae of S. glomerata were more resilient to elevated Pco2 than wild larvae. Measurement of the standard metabolic rate (SMR) of adult S. glomerata showed that at ambient Pco2, SMR is increased in selectively bred compared to wild oysters and is further increased during exposure to elevated Pco2. This study suggests that sensitive marine organisms may have the capacity to acclimate or adapt to elevated Pco2 over the next century and a change in energy turnover indicated by SMR may be a key process involved.” Laura M. Parker, Pauline M. Ross, Wayne A. O’Connor, Larissa Borysko, David A. Raftos, Hans-Otto Pörtner, Global Change Biology, DOI: 10.1111/j.1365-2486.2011.02520.x.

The Rate of Permafrost Carbon Release Under Aerobic and Anaerobic Conditions and its Potential Effects on Climate – Lee et al. (2011) “Recent observations suggest that permafrost thaw may create two completely different soil environments: aerobic in relatively well-drained uplands and anaerobic in poorly-drained wetlands. The soil oxygen availability will dictate the rate of permafrost carbon release as carbon dioxide (CO2) and as methane (CH4), and the overall effects of these emitted greenhouse gases on climate. The objective of this study was to quantify CO2 and CH4 release over a 500-day period from permafrost soil under aerobic and anaerobic conditions in the laboratory and to compare the potential effects of these emissions on future climate by estimating their relative climate forcing. We used permafrost soils collected from Alaska and Siberia with varying organic matter characteristics and simultaneously incubated them under aerobic and anaerobic conditions to determine rates of CO2 and CH4 production. Over 500 days of soil incubation at 15°C, we observed that carbon released under aerobic conditions was 3.9 to 10.0 times greater than anaerobic conditions. When scaled by greenhouse warming potential to account for differences between CO2 and CH4, relative climate forcing ranged 1.5-7.1. Carbon release in organic soils was nearly 20 times greater than mineral soils on a per gram soil basis, but when compared on a per gram carbon basis deep permafrost mineral soils showed a similar carbon release rates as organic soils for some soil types. This suggests that permafrost carbon may be very labile but that there are significant differences across soil types depending on the processes that controlled initial permafrost carbon accumulation within a particular landscape. Overall, our study showed that, independent of soil type, permafrost carbon in a relatively aerobic upland ecosystems may have a greater effect on climate as compared to a similar amount of permafrost carbon thawing in an anaerobic environment, despite the release of CH4 that occurs in anaerobic conditions.” Hanna Lee, Edward A. G. Schuur, Kanika S. Inglett, Martin Lavoie, Jeffrey P. Chanton, Global Change Biology, DOI: 10.1111/j.1365-2486.2011.02519.x.

New Willie Soon paper highlights solar effect to China temperatures

Variation in surface air temperature of China during the 20th century – Soon et al. (2011) “The 20th century surface air temperature (SAT) records of China from various sources are analyzed using data which include the recently-released Twentieth Century Reanalysis Project dataset. Two key features of the Chinese records are confirmed: (1) significant 1920 s and 1940 s warming in the temperature records, and (2) evidence for a persistent multi-decadal modulation of the Chinese surface temperature records in covariations with both incoming solar radiation at the top of the atmosphere as well as the modulated solar radiation reaching ground surface. New evidence is presented for this Sun-climate link for the instrumental record from 1880 to 2002. Additionally, two non-local physical aspects of solar radiation-induced modulation of the Chinese SAT record are documented and discussed. Teleconnections that provide a persistent and systematic modulation of the temperature response of the Tibetan Plateau and/or the tropospheric air column above the Eurasian continent (e.g., 30°N-70°N; 0°-120°E) are described. These teleconnections may originate from the solar irradiance-Arctic-North Atlantic Overturning Circulation mechanism proposed by Soon (2009). Also considered is the modulation of large-scale land-sea thermal contrasts both in terms of meridional and zonal gradients between the subtropical western Pacific and mid-latitude North Pacific and the continental landmass of China. The Circum-global Teleconnection (CGT) pattern of summer circulation of Ding and Wang (2005) provides a physical framework for study of the Sun-climate connection over East Asia. Our results highlight the importance of solar radiation reaching the ground and the concomitant importance of changes in atmospheric transparency or cloudiness or both in motivating a true physical explanation of any Sun-climate connection. We conclude that ground surface solar radiation is an important modulating factor for Chinese SAT changes on multidecadal to centennial timescales. Therefore, a comprehensive view of local and remote factors of climate change in China must take account of this as well as other natural and anthropogenic forcings.” Willie Soon, Koushik Dutta, David R. Legates, Victor Velasco and WeiJia Zhang, Journal of Atmospheric and Solar-Terrestrial Physics, doi:10.1016/j.jastp.2011.07.007.

A multi-diagnostic intercomparison of tropical width time series using reanalyses and satellite observations – Davis & Rosenlof (2011) “Poleward migration of the latitudinal edge of the tropics of ~0.25 – 3° decade−1 has been reported in several recent studies based on satellite and radiosonde data, and reanalysis output covering the past ~30 years. The goal of this paper is to identify the extent to which this large range of trends can be explained by the use of different data sources, time periods, and edge definitions, as well as how the widening varies as a function of hemisphere and season. Towards this end, we apply a suite of tropical edge latitude diagnostics based on tropopause height, winds, precipitation/evaporation, and outgoing longwave radiation (OLR) to several reanalyses and satellite data sets. These diagnostics include both previously used definitions and new definitions designed for more robust detection. The wide range of widening trends is shown to be primarily due to the use of different data sets and edge definitions, and only secondarily due to varying start/end dates. We also show that the large trends (> ~ 1° decade−1) previously reported in tropopause and OLR diagnostics are due to the use of subjective definitions based on absolute thresholds. Statistically significant Hadley cell expansion based on the mean meridional streamfunction of 1.0 – 1.5° decade−1 is found in three of four reanalyses that cover the full time period (1979–2009), whereas other diagnostics yield trends of −0.5 – 0.8° decade−1 that are mostly insignificant. There are indications of hemispheric and seasonal differences in the trends, but the differences are not statistically significant.” Sean M. Davis, Karen H. Rosenlof, Journal of Climate 2011, doi: 10.1175/JCLI-D-11-00127.1.

Stratosphere ozone recovery probably warms troposphere

Tropospheric temperature response to stratospheric ozone recovery in the 21st century – Hu et al. (2011) “Recent simulations predicted that the stratospheric ozone layer will likely return to pre-1980 levels in the middle of the 21st century, as a result of the decline of ozone depleting substances under the Montreal Protocol. Since the ozone layer is an important component in determining stratospheric and tropospheric-surface energy balance, the recovery of stratospheric ozone may have significant impact on tropospheric-surface climate. Here, using multi-model results from both the Intergovernmental Panel on Climate Change Fourth Assessment Report (IPCC-AR4) models and coupled chemistry-climate models, we show that as ozone recovery is considered, the troposphere is warmed more than that without considering ozone recovery, suggesting an enhancement of tropospheric warming due to ozone recovery. It is found that the enhanced tropospheric warming is mostly significant in the upper troposphere, with a global and annual mean magnitude of ~0.41 K for 2001–2050. We also find that relatively large enhanced warming occurs in the extratropics and polar regions in summer and autumn in both hemispheres, while the enhanced warming is stronger in the Northern Hemisphere than in the Southern Hemisphere. Enhanced warming is also found at the surface. The global and annual mean enhancement of surface warming is about 0.16 K for 2001–2050, with maximum enhancement in the winter Arctic.” Hu, Y., Xia, Y., and Fu, Q., Atmos. Chem. Phys., 11, 7687-7699, doi:10.5194/acp-11-7687-2011, 2011. [Full text]

Global and hemispheric temperature reconstruction from glacier length fluctuations – Leclercq & Oerlemans (2011) “Temperature reconstructions for recent centuries provide a historical context for the warming over the twentieth century. We reconstruct annual averaged surface temperatures of the past 400 years on hemispherical and global scale from glacier length fluctuations. We use the glacier length records of 308 glaciers. The reconstruction is a temperature proxy with decadal resolution that is completely independent of other temperature records. Temperatures are derived from glacier length changes using a linear response equation and an analytical glacier model that is calibrated on numerical model results. The global and hemispherical temperatures reconstructed from glacier length fluctuations are in good agreement with the instrumental record of the last century. Furthermore our results agree with existing multi-proxy reconstructions of temperature in the pre-instrumental period. The temperature record obtained from glacier fluctuations confirms the pronounced warming of the twentieth century, giving a global cumulative warming of 0.94 ± 0.31 K over the period 1830–2000 and a cumulative warming of 0.84 ± 0.35 K over the period 1600–2000.” Paul Willem Leclercq and Johannes Oerlemans, Climate Dynamics, DOI: 10.1007/s00382-011-1145-7. [Full text]

Using marine mammals to measure high latitude Atlantic temperatures

Temperature signature of high latitude Atlantic boundary currents revealed by marine mammal-borne sensor and Argo data – Grist et al. (2011) “Results from the development and analysis of a novel temperature dataset for the high latitude North-West Atlantic are presented. The new 1° gridded dataset (“ATLAS”) has been produced from about 13,000 Argo and 48,000 marine mammal (hooded seal, harp seal, grey seal and beluga) profiles spanning 2004–8. These data sources are highly complementary as marine mammals greatly enhance shelf region coverage where Argo floats are absent. ATLAS reveals distinctive boundary current related temperature minima in the Labrador Sea (−1.1°C) and at the east Greenland coast (1.8°C), largely absent in the widely-used Levitus’09 and EN3v2a datasets. The ATLAS 0–500 m average temperature is lower than Levitus’09 and EN3v2a by up to 3°C locally. Differences are strongest from 0–300 m and persist at reduced amplitude from 300–500 m. Our results clearly reveal the value of marine mammal-borne sensors for a reliable description of the North-West Atlantic at a time of rapid change.” Grist, J. P., S. A. Josey, L. Boehme, M. P. Meredith, F. J. M. Davidson, G. B. Stenson, and M. O. Hammill (2011), Geophys. Res. Lett., 38, L15601, doi:10.1029/2011GL048204.

Southern China extreme cold winter events getting rare

Extreme cold winter events in southern China during AD 1650–2000 – Zheng et al. (2011) “We defined extreme cold winter events as those with occurrence probabilities lower than the 10th percentile of the probability density function, based on observed winter temperatures in southern China since 1951. Subsequently, we constructed impact severity levels using documentary evidence for those events during 1951–2000, considering three indexes for the freezing of rivers/lakes, widespread snow/ice storms, and cold damage to subtropical/tropical crops. Using these criteria we identified 50 extreme cold winters for the period AD 1650–1949 based on ∼4000 pieces of comparable information extracted from local gazettes in southern China, after verification using data from three weather stations with long records. It was found that the frequencies of the extreme cold winter events since 1650 varied over time. The most frequent occurrences were found during AD 1650–1699 and in the first and second halves of the 19th century, with frequencies twice as high as in the second half of the 20th century. In contrast, the frequencies of extreme winters during the 18th century were close to that in the second half of the 20th century. High frequencies of extreme cold winters in AD 1650–1720 and AD 1795–1835 occurred during the sunspot Maunder and Dalton Minima. The intensities of some historical cold events, such as those during 1653–1654, 1670, 1690, 1861, 1892 and 1929, exceeded those of the coldest winter events since 1951.” Jingyun Zheng, Lingling Ding, Zhixin Hao, Quansheng Ge, Boreas, DOI: 10.1111/j.1502-3885.2011.00225.x.

Elevated CO2 has negative effect to wheat grain protein content

Yield vs. Quality trade-offs for wheat in response to carbon dioxide and ozone – Pleijel & Uddling (2011) “Although it is established that there exist potential trade-offs between grain yield and grain quality in wheat exposed to elevated carbon dioxide (CO2) and ozone (O3), their underlying causes remain poorly explored. To investigate the processes affecting grain quality under altered CO2 and O3, we analysed 57 experiments with CO2 or O3 exposure in different exposure systems. The study covered 24 cultivars studied in 112 experimental treatments from 11 countries. A significant growth dilution effect on grain protein was found: a change in grain yield of 10% by O3 was associated with a change in grain protein yield of 8.1% (R2 = 0.96), whereas a change in yield effect of 10% by CO2 was linked to a change in grain protein yield effect of 7.5% (R2 = 0.74). Superimposed on this effect, elevated CO2, but not O3, had a significant negative effect on grain protein yield also in the absence of effects on grain yield, indicating that there exists a process by which CO2 restricts grain protein accumulation, which is absent for O3. Grain mass, another quality trait, was more strongly affected by O3 than grain number, whereas the opposite was true for CO2. Harvest index was strongly and negatively influenced by O3, but was unaffected by CO2. We conclude that yield vs. protein trade-offs for wheat in response to CO2 and O3 are constrained by close relationships between effects on grain biomass and less than proportional effects on grain protein. An important and novel finding was that elevated CO2 has a direct negative effect on grain protein accumulation independent of the yield effect, supporting recent evidence of CO2-induced impairment of nitrate uptake/assimilation. Finally, our results demonstrated that processes underlying responses of grain yield vs. quality trade-offs are very different in wheat exposed to elevated O3 compared with elevated CO2.” Håkan Pleijel, Johan Uddling, Global Change Biology, DOI: 10.1111/j.1365-2486.2011.2489.x.

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This is a list of papers on recent decline and extinctions in amphibian populations. The list is not complete, and will most likely be updated in the future in order to make it more thorough and more representative.

Can amphibians take the heat? Vulnerability to climate warming in subtropical and temperate larval amphibian communities – Duarte et al. (2011) “Predicting the biodiversity impacts of global warming implies we know where and with what magnitude these impacts will be encountered. Amphibians are currently the most threatened vertebrates, mainly due to habitat loss and to emerging infectious diseases. Global warming may further exacerbate their decline in the near future, although the impact might vary geographically. We predicted that subtropical amphibians should be relatively susceptible to warming induced extinctions because their upper critical thermal limits (CTmax) might be only slightly higher than maximum pond temperatures (Tmax). We tested this prediction by measuring CTmax and Tmax for 47 larval amphibian species from two thermally distinct subtropical communities (the warm community of the Gran Chaco and the cool community of Atlantic Forest, northern Argentina), as well as from one European temperate community. Upper thermal tolerances of tadpoles were positively correlated (controlling for phylogeny) with maximum pond temperatures, although the slope was steeper in subtropical than in temperate species. CTmax values were lowest in temperate species and highest in the subtropical warm community, which paradoxically, had very low warming tolerance (CTmax – Tmax) and therefore may be prone to future local extinction from acute thermal stress if rising pond Tmax soon exceeds their CTmax. Canopy protected subtropical cool species have larger warming tolerance and thus should be less impacted by peak temperatures. Temperate species are relatively secure to warming impacts, except for late breeders with low thermal tolerance which may be exposed to physiological thermal stress in the coming years.” Helder Duarte, Miguel Tejedo, Marco Katzenberger, Federico Marangoni, Diego Baldo, Juan Francisco Beltrán, Dardo Andrea Martí, Alex Richter-Boix, Alejandro Gonzalez-Voyer, Global Change Biology, DOI: 10.1111/j.1365-2486.2011.02518.x.

Citation Rate and Perceived Subject Bias in the Amphibian-Decline Literature – Ohmer & Bishop (2011) “As a result of global declines in amphibian populations, interest in the conservation of amphibians has grown. This growth has been fueled partially by the recent discovery of other potential causes of declines, including chytridiomycosis (the amphibian chytrid, an infectious disease) and climate change. It has been proposed that researchers have shifted their focus to these novel stressors and that other threats to amphibians, such as habitat loss, are not being studied in proportion to their potential effects. We tested the validity of this proposal by reviewing the literature on amphibian declines, categorizing the primary topic of articles within this literature (e.g., habitat loss or UV-B radiation) and comparing citation rates among articles on these topics and impact factors of journals in which the articles were published. From 1990 to 2009, the proportion of papers on habitat loss remained fairly constant, and although the number of papers on chytridiomycosis increased after the disease was described in 1998, the number of published papers on amphibian declines also increased. Nevertheless, papers on chytridiomycosis were more highly cited than papers not on chytridiomycosis and were published in journals with higher impact factors on average, which may indicate this research topic is more popular in the literature. Our results were not consistent with a shift in the research agenda on amphibians. We believe the perception of such a shift has been supported by the higher citation rates of papers on chytridiomycosis.” Michel E. Ohmer, Phillip J. Bishop, Conservation Biology, Volume 25, Issue 1, pages 195–199, February 2011, DOI: 10.1111/j.1523-1739.2010.01591.x. [Full text, Supporting informationNote that SI has a spreadsheet with references to about 1500 papers on the subject!]

Amphibian decline and extinction: What we know and what we need to learn – Collins (2010) “For over 350 million yr, thousands of amphibian species have lived on Earth. Since the 1980s, amphibians have been disappearing at an alarming rate, in many cases quite suddenly. What is causing these declines and extinctions? In the modern era (post 1500) there are 6 leading causes of biodiversity loss in general, and all of these acting alone or together are responsible for modern amphibian declines: commercial use; introduced/exotic species that compete with, prey on, and parasitize native frogs and salamanders; land use change; contaminants; climate change; and infectious disease. The first 3 causes are historical in the sense that they have been operating for hundreds of years, although the rate of change due to each accelerated greatly after about the mid-20th century. Contaminants, climate change, and emerging infectious diseases are modern causes suspected of being responsible for the so-called ‘enigmatic decline’ of amphibians in protected areas. Introduced/exotic pathogens, land use change, and infectious disease are the 3 causes with a clear role in amphibian decline as well as extinction; thus far, the other 3 causes are only implicated in decline and not extinction. The present work is a review of the 6 causes with a focus on pathogens and suggested areas where new research is needed. Batrachochytrium dendrobatidis (Bd) is a chytrid fungus that is an emerging infectious disease causing amphibian population decline and species extinction. Historically, pathogens have not been seen as a major cause of extinction, but Bd is an exception, which is why it is such an interesting, important pathogen to understand. The late 20th and early 21st century global biodiversity loss is characterized as a sixth extinction event. Amphibians are a striking example of these losses as they disappear at a rate that greatly exceeds historical levels. Consequently, modern amphibian decline and extinction is a lens through which we can view the larger story of biodiversity loss and its consequences.” James P. Collins, Dis Aquat Org 92:93-99, doi:10.3354/dao02307.

Tropical cloud forest climate variability and the demise of the Monteverde golden toad – Anchukaitis & Evans (2010) “Widespread amphibian extinctions in the mountains of the American tropics have been blamed on the interaction of anthropogenic climate change and a lethal pathogen. However, limited meteorological records make it difficult to conclude whether current climate conditions at these sites are actually exceptional in the context of natural variability. We use stable oxygen isotope measurements from trees without annual rings to reconstruct a century of hydroclimatology in the Monteverde Cloud Forest of Costa Rica. High-resolution measurements reveal coherent isotope cycles that provide annual chronological control and paleoclimate information. Climate variability is dominated by interannual variance in dry season moisture associated with El Niño Southern Oscillation events. There is no evidence of a trend associated with global warming. Rather, the extinction of the Monteverde golden toad (Bufo periglenes) appears to have coincided with an exceptionally dry interval caused by the 1986–1987 El Niño event.” Kevin J. Anchukaitis and Michael N. Evans, PNAS March 16, 2010 vol. 107 no. 11 5036-5040, doi: 10.1073/pnas.0908572107. [Full text]

Global Amphibian Extinction Risk Assessment for the Panzootic Chytrid Fungus – Rödder et al. (2009) “Species are being lost at increasing rates due to anthropogenic effects, leading to the recognition that we are witnessing the onset of a sixth mass extinction. Emerging infectious disease has been shown to increase species loss and any attempts to reduce extinction rates need to squarely confront this challenge. Here, we develop a procedure for identifying amphibian species that are most at risk from the effects of chytridiomycosis by combining spatial analyses of key host life-history variables with the pathogen’s predicted distribution. We apply our rule set to the known global diversity of amphibians in order to prioritize pecies that are most at risk of loss from disease emergence. This risk assessment shows where limited conservation funds are best deployed in order to prevent further loss of species by enabling ex situ amphibian salvage operations and focusing any potential disease mitigation projects.” Dennis Rödder, Jos Kielgast, Jon Bielby, Sebastian Schmidtlein, Jaime Bosch, Trenton W. J. Garner, Michael Veith, Susan Walker, Matthew C. Fisher and Stefan Lötters, Diversity 2009, 1(1), 52-66; doi:10.3390/d1010052. [Full text]

Chytridiomycosis, Amphibian Extinctions, and Lessons for the Prevention of Future Panzootics – Kriger & Hero (2009) “The human-mediated transport of infected amphibians is the most plausible driver for the intercontinental spread of chytridiomycosis, a recently emerged infectious disease responsible for amphibian population declines and extinctions on multiple continents. Chytridiomycosis is now globally ubiquitous, and it cannot be eradicated from affected sites. Its rapid spread both within and between continents provides a valuable lesson on preventing future panzootics and subsequent erosion of biodiversity, not only of amphibians, but of a wide array of taxa: the continued inter-continental trade and transport of animals will inevitably lead to the spread of novel pathogens, followed by numerous extinctions. Herein, we define and discuss three levels of amphibian disease management: (1) post-exposure prophylactic measures that are curative in nature and applicable only in a small number of situations; (2) pre-exposure prophylactic measures that reduce disease threat in the short-term; and (3) preventive measures that remove the threat altogether. Preventive measures include a virtually complete ban on all unnecessary long-distance trade and transport of amphibians, and are the only method of protecting amphibians from disease-induced declines and extinctions over the long-term. Legislation to prevent the emergence of new diseases is urgently required to protect global amphibian biodiversity.” Kerry M. Kriger and Jean-Marc Hero, EcoHealth, Volume 6, Number 1, 6-10, DOI: 10.1007/s10393-009-0228-y. [Full text]

Are we in the midst of the sixth mass extinction? A view from the world of amphibians – Wake & Vredenburg (2008) “Many scientists argue that we are either entering or in the midst of the sixth great mass extinction. Intense human pressure, both direct and indirect, is having profound effects on natural environments. The amphibians—frogs, salamanders, and caecilians—may be the only major group currently at risk globally. A detailed worldwide assessment and subsequent updates show that one-third or more of the 6,300 species are threatened with extinction. This trend is likely to accelerate because most amphibians occur in the tropics and have small geographic ranges that make them susceptible to extinction. The increasing pressure from habitat destruction and climate change is likely to have major impacts on narrowly adapted and distributed species. We show that salamanders on tropical mountains are particularly at risk. A new and significant threat to amphibians is a virulent, emerging infectious disease, chytridiomycosis, which appears to be globally distributed, and its effects may be exacerbated by global warming. This disease, which is caused by a fungal pathogen and implicated in serious declines and extinctions of >200 species of amphibians, poses the greatest threat to biodiversity of any known disease. Our data for frogs in the Sierra Nevada of California show that the fungus is having a devastating impact on native species, already weakened by the effects of pollution and introduced predators. A general message from amphibians is that we may have little time to stave off a potential mass extinction.” David B. Wake and Vance T. Vredenburg, PNAS August 12, 2008 vol. 105 no. Supplement 1 11466-11473, doi: 10.1073/pnas.0801921105. [Full text]

Evaluating the links between climate, disease spread, and amphibian declines – Rohr et al. (2008) “Human alteration of the environment has arguably propelled the Earth into its sixth mass extinction event and amphibians, the most threatened of all vertebrate taxa, are at the forefront. Many of the worldwide amphibian declines have been caused by the chytrid fungus, Batrachochytrium dendrobatidis (Bd), and two contrasting hypotheses have been proposed to explain these declines. Positive correlations between global warming and Bd-related declines sparked the chytrid-thermal-optimum hypothesis, which proposes that global warming increased cloud cover in warm years that drove the convergence of daytime and nighttime temperatures toward the thermal optimum for Bd growth. In contrast, the spatiotemporal-spread hypothesis states that Bd-related declines are caused by the introduction and spread of Bd, independent of climate change. We provide a rigorous test of these hypotheses by evaluating (i) whether cloud cover, temperature convergence, and predicted temperature-dependent Bd growth are significant positive predictors of amphibian extinctions in the genus Atelopus and (ii) whether spatial structure in the timing of these extinctions can be detected without making assumptions about the location, timing, or number of Bd emergences. We show that there is spatial structure to the timing of Atelopus spp. extinctions but that the cause of this structure remains equivocal, emphasizing the need for further molecular characterization of Bd. We also show that the reported positive multi-decade correlation between Atelopus spp. extinctions and mean tropical air temperature in the previous year is indeed robust, but the evidence that it is causal is weak because numerous other variables, including regional banana and beer production, were better predictors of these extinctions. Finally, almost all of our findings were opposite to the predictions of the chytrid-thermal-optimum hypothesis. Although climate change is likely to play an important role in worldwide amphibian declines, more convincing evidence is needed of a causal link.” Jason R. Rohr, Thomas R. Raffel, John M. Romansic, Hamish McCallum, and Peter J. Hudson, PNAS November 11, 2008 vol. 105 no. 45 17436-17441, doi: 10.1073/pnas.0806368105. [Full text]

Life-history trade-offs influence disease in changing climates: strategies of an amphibian pathogen – Woodhams et al. (2008) “Life-history trade-offs allow many animals to maintain reproductive fitness across a range of climatic conditions. When used by parasites and pathogens, these strategies may influence patterns of disease in changing climates. The chytrid fungus, Batrachochytrium dendrobatidis, is linked to global declines of amphibian populations. Short-term growth in culture is maximal at 17°–25°C. This has been used in an argument that global warming, which increases the time that amphibians spend at these temperatures in cloud-covered montane environments, has led to extinctions. Here we show that the amphibian chytrid responds to decreasing temperatures with trade-offs that increase fecundity as maturation rate slows and increase infectivity as growth decreases. At 17°–25°C, infectious zoospores encyst (settle and develop a cell wall) and develop into the zoospore-producing stage (zoosporangium) faster, while at 7°–10°C, greater numbers of zoospores are produced per zoosporangium; these remain infectious for a longer period of time. We modeled the population growth of B. dendrobatidis through time at various temperatures using delayed differential equations and observational data for four parameters: developmental rate of thalli, fecundity, rate of zoospore encystment, and rate of zoospore survival. From the models, it is clear that life-history trade-offs allow B. dendrobatidis to maintain a relatively high long-term growth rate at low temperatures, so that it maintains high fitness across a range of temperatures. When a seven-day cold shock is simulated, the outcome is intermediate between the two constant temperature regimes, and in culture, a sudden drop in temperature induces zoospore release. These trade-offs can be ecologically important for a variety of organisms with complex life histories, including pathogenic microorganisms. The effect of temperature on amphibian mortality will depend on the interaction between fungal growth and host immune function and will be modified by host ecology, behavior, and life history. These results demonstrate that B. dendrobatidis populations can grow at high rates across a broad range of environmental temperatures and help to explain why it is so successful in cold montane environments.” Woodhams, Douglas C., Ross A. Alford, Cheryl J. Briggs, Megan Johnson, and Louise A. Rollins-Smith. 2008, Ecology 89:1627–1639. [doi:10.1890/06-1842.1]. [Full text]

Measuring the Meltdown: Drivers of Global Amphibian Extinction and Decline – Sodhi et al. (2008) “Habitat loss, climate change, over-exploitation, disease and other factors have been hypothesised in the global decline of amphibian biodiversity. However, the relative importance of and synergies among different drivers are still poorly understood. We present the largest global analysis of roughly 45% of known amphibians (2,583 species) to quantify the influences of life history, climate, human density and habitat loss on declines and extinction risk. Multi-model Bayesian inference reveals that large amphibian species with small geographic range and pronounced seasonality in temperature and precipitation are most likely to be Red-Listed by IUCN. Elevated habitat loss and human densities are also correlated with high threat risk. Range size, habitat loss and more extreme seasonality in precipitation contributed to decline risk in the 2,454 species that declined between 1980 and 2004, compared to species that were stable (n=1,545) or had increased (n=28). These empirical results show that amphibian species with restricted ranges should be urgently targeted for conservation.” Navjot S. Sodhi, David Bickford, Arvin C. Diesmos, Tien Ming Lee, Lian Pin Koh, Barry W. Brook, Cagan H. Sekercioglu, and Corey J. A. Bradshaw, PLoS ONE. 2008; 3(2): e1636, doi: 10.1371/journal.pone.0001636. [Full text]

Global warming and amphibian extinctions in eastern Australia – Laurance (2008) “Pounds et al. recently argued that the dramatic, fungal pathogen-linked extinctions of numerous harlequin frogs (Atelopus spp.) in upland rainforests of South America mostly occurred immediately following exceptionally warm years, implicating global warming as a likely trigger for these extinctions. I tested this hypothesis using temperature data for eastern Australia, where at least 14 upland-rainforest frog species have also experienced extinctions or striking population declines attributed to the same fungal pathogen, and where temperatures have also risen significantly in recent decades. My analyses provide little direct support for the warm-year hypothesis of Pounds et al., although my statistical power to detect effects of small (0.5°C) temperature increases was limited. However, I found stronger support for a modified version of the warm-year hypothesis, whereby frog declines were likely to occur following three consecutive years of unusually warm weather. This trend was apparent only at tropical latitudes, where rising minimum temperatures were greatest. Although much remains uncertain, my findings appear consistent with the notion that global warming could predispose some upland amphibian populations to virulent pathogens.” William F. Laurance, Austral Ecology, Volume 33, Issue 1, pages 1–9, February 2008, DOI: 10.1111/j.1442-9993.2007.01812.x. [Full text]

Riding the Wave: Reconciling the Roles of Disease and Climate Change in Amphibian Declines – Lips et al. (2008) “We review the evidence for the role of climate change in triggering disease outbreaks of chytridiomycosis, an emerging infectious disease of amphibians. Both climatic anomalies and disease-related extirpations are recent phenomena, and effects of both are especially noticeable at high elevations in tropical areas, making it difficult to determine whether they are operating separately or synergistically. We compiled reports of amphibian declines from Lower Central America and Andean South America to create maps and statistical models to test our hypothesis of spatiotemporal spread of the pathogen Batrachochytrium dendrobatidis (Bd), and to update the elevational patterns of decline in frogs belonging to the genus Atelopus. We evaluated claims of climate change influencing the spread of Bd by including error into estimates of the relationship between air temperature and last year observed. Available data support the hypothesis of multiple introductions of this invasive pathogen into South America and subsequent spread along the primary Andean cordilleras. Additional analyses found no evidence to support the hypothesis that climate change has been driving outbreaks of amphibian chytridiomycosis, as has been posited in the climate-linked epidemic hypothesis. Future studies should increase retrospective surveys of museum specimens from throughout the Andes and should study the landscape genetics of Bd to map fine-scale patterns of geographic spread to identify transmission routes and processes.” Karen R. Lips, Jay Diffendorfer, Joseph R. Mendelson III, Michael W. Sears, PLoS Biol 6(3): e72. doi:10.1371/journal.pbio.0060072. [Full text]

Amphibian Decline or Extinction? Current Declines Dwarf Background Extinction Rate – McCallum (2007) “Amphibian declines and extinctions are critical concerns of biologists around the world. The estimated current rate of amphibian extinction is known, but how it compares to the background amphibian extinction rate from the fossil record has not been well studied. I compared current amphibian extinction rates with their reported background extinction rates using standard and fuzzy arithmetic. These calculations suggest that the current extinction rate of amphibians could be 211 times the background amphibian extinction rate. If current estimates of amphibian species in imminent danger of extinction are included in these calculations, then the current amphibian extinction rate may range from 25,039–45,474 times the background extinction rate for amphibians. It is difficult to explain this unprecedented and accelerating rate of extinction as a natural phenomenon.” Malcolm L. McCallum, Journal of Herpetology 41(3):483-491. 2007, doi: 10.1670/0022-1511(2007)41[483:ADOECD]2.0.CO;2. [Full text]

Spread of Chytridiomycosis Has Caused the Rapid Global Decline and Extinction of Frogs – Skerratt et al. (2007) “The global emergence and spread of the pathogenic, virulent, and highly transmissible fungus Batrachochytrium dendrobatidis, resulting in the disease chytridiomycosis, has caused the decline or extinction of up to about 200 species of frogs. Key postulates for this theory have been completely or partially fulfilled. In the absence of supportive evidence for alternative theories despite decades of research, it is important for the scientific community and conservation agencies to recognize and manage the threat of chytridiomycosis to remaining species of frogs, especially those that are naive to the pathogen. The impact of chytridiomycosis on frogs is the most spectacular loss of vertebrate biodiversity due to disease in recorded history.” Lee Francis Skerratt, Lee Berger, Richard Speare, Scott Cashins, Keith Raymond McDonald, Andrea Dawn Phillott, Harry Bryan Hines and Nicole Kenyon, EcoHealth, Volume 4, Number 2, 125-134, DOI: 10.1007/s10393-007-0093-5. [Full text]

Widespread amphibian extinctions from epidemic disease driven by global warming – Pounds et al. (2006) “As the Earth warms, many species are likely to disappear, often because of changing disease dynamics. Here we show that a recent mass extinction associated with pathogen outbreaks is tied to global warming. Seventeen years ago, in the mountains of Costa Rica, the Monteverde harlequin frog (Atelopus sp.) vanished along with the golden toad (Bufo periglenes). An estimated 67% of the 110 or so species of Atelopus, which are endemic to the American tropics, have met the same fate, and a pathogenic chytrid fungus (Batrachochytrium dendrobatidis) is implicated. Analysing the timing of losses in relation to changes in sea surface and air temperatures, we conclude with ‘very high confidence’ (> 99%, following the Intergovernmental Panel on Climate Change, IPCC) that large-scale warming is a key factor in the disappearances. We propose that temperatures at many highland localities are shifting towards the growth optimum of Batrachochytrium, thus encouraging outbreaks. With climate change promoting infectious disease and eroding biodiversity, the urgency of reducing greenhouse-gas concentrations is now undeniable.” J. Alan Pounds, Martín R. Bustamante, Luis A. Coloma, Jamie A. Consuegra, Michael P. L. Fogden, Pru N. Foster, Enrique La Marca, Karen L. Masters, Andrés Merino-Viteri, Robert Puschendorf, Santiago R. Ron, G. Arturo Sánchez-Azofeifa, Christopher J. Still & Bruce E. Young, Nature 439, 161-167 (12 January 2006) | doi:10.1038/nature04246. [Full text]

Emerging infectious disease and the loss of biodiversity in a Neotropical amphibian community – Lips et al. (2006) “Pathogens rarely cause extinctions of host species, and there are few examples of a pathogen changing species richness and diversity of an ecological community by causing local extinctions across a wide range of species. We report the link between the rapid appearance of a pathogenic chytrid fungus Batrachochytrium dendrobatidis in an amphibian community at El Copé, Panama, and subsequent mass mortality and loss of amphibian biodiversity across eight families of frogs and salamanders. We describe an outbreak of chytridiomycosis in Panama and argue that this infectious disease has played an important role in amphibian population declines. The high virulence and large number of potential hosts of this emerging infectious disease threaten global amphibian diversity.” Karen R. Lips, Forrest Brem, Roberto Brenes, John D. Reeve, Ross A. Alford, Jamie Voyles, Cynthia Carey, Lauren Livo, Allan P. Pessier, and James P. Collins, PNAS February 28, 2006 vol. 103 no. 9 3165-3170, doi: 10.1073/pnas.0506889103. [Full text]

Species Review of Amphibian Extinction Risks in Madagascar: Conclusions from the Global Amphibian Assessment – Andreone et al. (2005) “We assessed the extinction risks of Malagasy amphibians by evaluating their distribution, occurrence in protected areas, population trends, habitat quality, and prevalence in commercial trade. We estimated and mapped the distribution of each of the 220 described Malagasy species and applied, for the first time, the IUCN Red List categories and criteria to all species described at the time of the assessment. Nine species were categorized as critically endangered, 21 as endangered, and 25 as vulnerable. The most threatened species occur on the High Plateau and/or have been subjected to overcollection for the pet trade, but restricted extent of occurrence and ongoing habitat destruction were identified as the most important factors influencing extinction threats. The two areas with the majority of threatened species were the northern Tsaratanana-Marojejy-Masoala highlands and the southeastern Anosy Mountains. The current system of protected areas includes 82% of the threatened amphibian species. Of the critically endangered species, 6 did not occur in any protected area. For conservation of these species we recommend the creation of a reserve for the species of the Mantella aurantiaca group, the inclusion of two Scaphiophryne species in the Convention on the International Trade in Endangered Species Appendix II, and the suspension of commercial collecting for Mantella cowani. Field surveys during the last 15 years reveal no pervasive extinction of Malagasy amphibians resulting from disease or other agents, as has been reported in some other areas of the world.” Franco Andreone, John E. Cadle, Neil Cox, Frank Glaw, Ronald A. Nussbaum, Christopher J. Raxworthy, Simon N. Stuart, Denis Vallan, Miguel Vences, Conservation Biology, Volume 19, Issue 6, pages 1790–1802, December 2005, DOI: 10.1111/j.1523-1739.2005.00249.x. [Full text]

Status and Trends of Amphibian Declines and Extinctions Worldwide – Stuart et al. (2004) “The first global assessment of amphibians provides new context for the well-publicized phenomenon of amphibian declines. Amphibians are more threatened and are declining more rapidly than either birds or mammals. Although many declines are due to habitat loss and overutilization, other, unidentified processes threaten 48% of rapidly declining species and are driving species most quickly to extinction. Declines are nonrandom in terms of species’ ecological preferences, geographic ranges, and taxonomic associations and are most prevalent among Neotropical montane, stream-associated species. The lack of conservation remedies for these poorly understood declines means that hundreds of amphibian species now face extinction.” Simon N. Stuart, Janice S. Chanson, Neil A. Cox, Bruce E. Young, Ana S. L. Rodrigues, Debra L. Fischman and Robert W. Waller, Science 3 December 2004: Vol. 306 no. 5702 pp. 1783-1786, DOI: 10.1126/science.1103538. [Full text]

Chytridiomycosis causes amphibian mortality associated with population declines in the rain forests of Australia and Central America – Berger et al. (1998) “Epidermal changes caused by a chytridiomycete fungus (Chytridiomycota; Chytridiales) were found in sick and dead adult anurans collected from montane rain forests in Queensland (Australia) and Panama during mass mortality events associated with significant population declines. We also have found this new disease associated with morbidity and mortality in wild and captive anurans from additional locations in Australia and Central America. This is the first report of parasitism of a vertebrate by a member of the phylum Chytridiomycota. Experimental data support the conclusion that cutaneous chytridiomycosis is a fatal disease of anurans, and we hypothesize that it is the proximate cause of these recent amphibian declines.” Lee Berger, Rick Speare, Peter Daszak, D. Earl Green, Andrew A. Cunningham, C. Louise Goggin, Ron Slocombe, Mark A. Ragan, Alex D. Hyatt, Keith R. McDonald, Harry B. Hines, Karen R. Lips, Gerry Marantelli, and Helen Parkes, PNAS July 21, 1998 vol. 95 no. 15 9031-9036. [Full text]

Amphibian Declines: Judging Stability, Persistence, and Susceptibility of Populations to Local and Global Extinctions – Blaustein et al. (1994) “Extinctions are normal biological phenomena. Both mass extinctions in geological time and local extinctions in ecological time are well documented, but rates of extinction have increased in recent years – especially in vertebrates, including amphibians – as illustrated by recent reports of their population declines and range reductions. We suggest that long-term population data are necessary for rigorously evaluating the significance of the amphibian declines. Due to the physiological constraints, relatively low mobility, and site fidelity of amphibians, we suggest that many amphibian populations may be unable to recolonize areas after local extinction.” Andrew R. Blaustein, David B. Wake and Wayne P. Sousa, Conservation Biology, Vol. 8, No. 1 (Mar., 1994), pp. 60-71. [Full text]

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Here is the new research published last week. I’m not including everything that was published but just some papers that got my attention. Those who follow my Facebook page (and/or Twitter) have already seen most of these, as I post these there as soon as they are published. Here, I’ll just put them out in one batch. Sometimes I might also point out to some other news as well, but the new research will be the focus here. Here’s the archive for the news of previous weeks. By the way, if this sort of thing interests you, be sure to check out A Few Things Illconsidered, they have a weekly posting containing lots of links to new research and other climate related news. Planet 3.0 also reports new research.

Published last week:

Circumpolar greening may provide positive feedback to warming

Greening in the circumpolar high-latitude may amplify warming in the growing season – Jeong et al. (2011) “We present a study that suggests greening in the circumpolar high-latitude regions amplifies surface warming in the growing season (May–September) under enhanced greenhouse conditions. The investigation used a series of climate simulations with the Community Atmospheric Model version 3—which incorporates a coupled, dynamic global vegetation model—with and without vegetation feedback, under both present and doubled CO2 concentrations. Results indicate that climate warming and associated changes promote circumpolar greening with northward expansion and enhanced greenness of both the Arctic tundra and boreal forest regions. This leads to additional surface warming in the high-latitudes in the growing season, primarily through more absorption of incoming solar radiation. The resulting surface and tropospheric warming in the high-latitude and Arctic regions weakens prevailing tropospheric westerlies over 45–70N, leading to the formation of anticyclonic pressure anomalies in the Arctic regions. These pressure anomalies resemble the anomalous circulation pattern during the negative phase of winter Arctic Oscillation. It is suggested that these circulation anomalies reinforce the high-latitude and Arctic warming in the growing season.” Jee-Hoon Jeong, Jong-Seong Kug, Baek-Min Kim, Seung-Ki Min, Hans W. Linderholm, Chang-Hoi Ho, David Rayner, Deliang Chen and Sang-Yoon Jun, Climate Dynamics, DOI: 10.1007/s00382-011-1142-x.

Few years without upper ocean warming is not exceptional

Tracing the upper ocean’s “missing heat” – Katsman & van Oldenborgh (2011) “Over the period 2003–2010, the upper ocean has not gained any heat, despite the general expectation that the ocean will absorb most of the Earth’s current radiative imbalance. Answering to what extent this heat was transferred to other components of the climate system and by what process(-es) gets to the essence of understanding climate change. Direct heat flux observations are too inaccurate to assess such exchanges. In this study we therefore trace these heat budget variations by analyzing an ensemble of climate model simulations. The analysis reveals that an 8-yr period without upper ocean warming is not exceptional. It is explained by increased radiation to space (45%), largely as a result of El Niño variability on decadal timescales, and by increased ocean warming at larger depths (35%), partly due to a decrease in the strength of the Atlantic meridional overturning circulation. Recently-observed changes in these two large-scale modes of climate variability point to an upcoming resumption of the upward trend in upper ocean heat content.” Katsman, C. A., and G. J. van Oldenborgh (2011), Geophys. Res. Lett., 38, L14610, doi:10.1029/2011GL048417. [Full text]

Exchange of groundwater and surface-water mediated by permafrost response to seasonal and long term air temperature variation – Ge et al. (2011) “Permafrost dynamics impact hydrologic cycle processes by promoting or impeding groundwater and surface water exchange. Under seasonal and decadal air temperature variations, permafrost temperature changes control the exchanges between groundwater and surface water. A coupled heat transport and groundwater flow model, SUTRA, was modified to simulate groundwater flow and heat transport in the subsurface containing permafrost. The northern central Tibet Plateau was used as an example of model application. Modeling results show that in a yearly cycle, groundwater flow occurs in the active layer from May to October. Maximum groundwater discharge to the surface lags the maximum subsurface temperature by two months. Under an increasing air temperature scenario of 3°C per 100 years, over the initial 40-year period, the active layer thickness can increase by three-fold. Annual groundwater discharge to the surface can experience a similar three-fold increase in the same period. An implication of these modeling results is that with increased warming there will be more groundwater flow in the active layer and therefore increased groundwater discharge to rivers. However, this finding only holds if sufficient upgradient water is available to replenish the increased discharge. Otherwise, there will be an overall lowering of the water table in the recharge portion of the catchment.” Ge, S., J. McKenzie, C. Voss, and Q. Wu (2011), Geophys. Res. Lett., 38, L14402, doi:10.1029/2011GL047911.

Early summer intense typhoons new feature of North Pacific since 2000

An abrupt increase of intense typhoons over the western North Pacific in early summer – Tu et al. (2011) “The frequency and intensity of typhoons have been a focus in studying typhoon-related climate changes. In this study, we focus on a seasonal cycle of intense typhoons (category 4 and 5) over the western North Pacific, particularly changes in the number of intense typhoons in early summer. In general, 81% of intense typhoons occur in July–November (JASON), with maxima in September and October. Our analysis shows that intense typhoons have tended to occur more frequently in May since the year 2000. Before 2000, intense typhoons seldom occurred in May, with a frequency of around once per decade. After 2000, however, the frequency of intense typhoons has become much higher in May—almost once per year. We have also examined changes in the large-scale environment in the past few decades. The results show that the large-scale environment did become more favorable for intense typhoons in the 2000s, which is consistent with a larger tropical cyclone genesis index. The changes include warmer sea surface temperature, higher sea surface height, larger upper-ocean heat content, weaker vertical wind shear, increased tropospheric water vapor, and greater water vapor in the mid-troposphere. The last two might be more important than the others.” Jien-Yi Tu et al 2011 Environ. Res. Lett. 6 034013 doi: 10.1088/1748-9326/6/3/034013. [Full text]

How fast oceans reach thermal equilibrium?

Equilibrium thermal response timescale of global oceans – Yang & Zhu (2011) “The equilibrium response timescale of global oceans is estimated in a fully coupled climate model. In general, the equilibrium timescale increases with depth, except in the polar region. The timescale is approximately 200 years for the ocean for depths above 1 km, and it increases to 1500 years at a depth of 3 km. A layer with a rapid timescale change, referred to as a temporacline, is located at a depth of 1.5–2 km, which is analogous to the permanent thermocline in the ocean. The equilibrium timescale varies with the sign of the change in radiative forcing. The ocean response to surface cooling could be twice as fast as the surface warming because of enhanced vertical mixing, convection and overturning circulation. However, this phenomenon only occurs below the Atlantic temporacline. For the Atlantic upper ocean, the timescale is longer in the cooling case because of the readjustment of the upper ocean to the enhanced Atlantic overturning circulation. In the Pacific, the timescale change in the warming and cooling cases is not as significant as in the Atlantic because of the lack of deep convection.” Yang, H., and J. Zhu (2011), Geophys. Res. Lett., 38, L14711, doi:10.1029/2011GL048076.

Expected adaptation to global warming observed in Cepaea nemoralis

Evolutionary change in Cepaea nemoralis shell colour over 43 years – Ożgo & Schilthuizen (2011) “We compared shell colour forms in the land snail Cepaea nemoralis at 16 sites in a 7 × 8 km section of the Province of Groningen, the Netherlands, between 1967 and 2010. To do so, we used stored samples in a natural history collection and resampled the exact collection localities. We found that almost all populations had experienced considerable evolutionary change in various phenotypes, possibly due to population bottlenecks and habitat change after repeated land consolidation schemes in the area. More importantly, we found a consistent increase in yellow effectively unbanded snails at the expense of brown snails. This is one of the expected adaptations to climate change (this area of The Netherlands has warmed by 1.5 – 2.0 °C over the time period spanned by the two sampling years), and the first clear demonstration of this in C. nemoralis.” Małgorzata Ożgo, Menno Schilthuizen, Global Change Biology, DOI: 10.1111/j.1365-2486.2011.02514.x.

When will global warming show up locally?

Early onset of significant local warming in low latitude countries – Mahlstein et al. (2011) “The Earth is warming on average, and most of the global warming of the past half-century can very likely be attributed to human influence. But the climate in particular locations is much more variable, raising the question of where and when local changes could become perceptible enough to be obvious to people in the form of local warming that exceeds interannual variability; indeed only a few studies have addressed the significance of local signals relative to variability. It is well known that the largest total warming is expected to occur in high latitudes, but high latitudes are also subject to the largest variability, delaying the emergence of significant changes there. Here we show that due to the small temperature variability from one year to another, the earliest emergence of significant warming occurs in the summer season in low latitude countries (≈25°S–25°N). We also show that a local warming signal that exceeds past variability is emerging at present, or will likely emerge in the next two decades, in many tropical countries. Further, for most countries worldwide, a mean global warming of 1 °C is sufficient for a significant temperature change, which is less than the total warming projected for any economically plausible emission scenario. The most strongly affected countries emit small amounts of CO2 per capita and have therefore contributed little to the changes in climate that they are beginning to experience.” I Mahlstein et al 2011 Environ. Res. Lett. 6 034009 doi: 10.1088/1748-9326/6/3/034009. [Full text]

Urban warming has been higher than greenhouse warming over South Korea

Quantitative Estimates of Warming by Urbanization in South Korea over the Past 55 Years (1954-2008) – Kim & Kim (2011) “The quantitative values of the urban warming effect over city stations in the Korean peninsula were estimated by using the warming mode of Empirical Orthogonal Function (EOF) analysis of 55 years of temperature data, from 1954 to 2008. The estimated amount of urban warming was verified by applying the multiple linear regression equation with two independent variables: the rate of population growth and the total population. Through the multiple linear regression equation, we obtained a significance level of 0.05% and a coefficient of determination of 0.60. This means that it is somewhat liable to the estimated effects of urbanization, in spite of the settings of some supposition. The cities that show great warming due to urbanization are Daegu, Pohang, Seoul, and Incheon, which show values of about 1.35, 1.17, 1.16, and 1.10°C, respectively. The areas that showed urban warming less than 0.2°C are Chupungnyeong and Mokpo. On average, the total temperature increase over South Korea was about 1.37 °C; the amount of increase caused by the greenhouse effect is approximately 0.60 °C, and the amount caused by urban warming is approximately 0.77 °C.” Maeng-Ki Kim and Seonae Kim, Atmospheric Environment, doi:10.1016/j.atmosenv.2011.07.028.

Middle Würmian in the Alps had to be warmer than it is today

Was the Middle Würmian in the High Alps warmer than today? – Döppes et al. (2011) “This study presents a cohesive review of the existing radiometric data as well as morphological and genetic analysis of bear remains from ten high-alpine caves, mostly from the Middle Würmian Interstadial complex, roughly corresponding to the marine isotope stage (MIS) 3 and dating back between 65,000-30,000 years before present. Today these caves are located in an area without any vegetation, which could not provide the herbivorous bears with sufficient food resources. It therefore can be concluded that the Middle Würmian in the Alps had to be warmer than it is today. Furthermore, congruent and conflicting data from soil formation in loess sequences as well as sinter data in caves are discussed in more detail to evaluate this hypothesis.” Doris Döppes, Gernot Rabeder and Mathias Stiller, Quaternary International, doi:10.1016/j.quaint.2011.07.029.

Sea ice trends in the Antarctic and their relationship to surface air temperature during 1979–2009 – Shu et al. (2011) “Surface air temperature (SAT) from four reanalysis/analysis datasets are analyzed and compared with the observed SAT from 11 stations in the Antarctic. It is found that the SAT variation from Goddard Institute for Space Studies (GISS) is the best to represent the observed SAT. Then we use the sea ice concentration (SIC) data from satellite measurements, the SAT data from the GISS dataset and station observations to examine the trends and variations of sea ice and SAT in the Antarctic during 1979–2009. The Antarctic sea ice extent (SIE) shows an increased trend during 1979–2009, with a trend rate of 1.36 ± 0.43% per decade. Ensemble empirical mode decomposition analysis shows that the rate of the increased trend has been accelerating in the past decade. Antarctic SIE trend depends on the season, with the maximum increase occurring in autumn. If the relationship between SIC and GISS SAT trends is examined regionally, Antarctic SIC trends agree well with the local SAT trends in the most Antarctic regions. That is, Antarctic SIC and SAT show an inverse relationship: a cooling (warming) SAT trend is associated with an upward (downward) SIC trend. It is also concluded that the relationship between sea ice and SAT trends in the Antarctic should be examined regionally rather than integrally.” Qi Shu, Fangli Qiao, Zhenya Song and Chunzai Wang, Climate Dynamics, DOI: 10.1007/s00382-011-1143-9. [Full text]